Semiconductor device tester

ABSTRACT

In one aspect, the present invention is a system and method for obtaining information regarding one or more contact holes and/or vias on a semiconductor wafer. In this regard, in one embodiment, the system comprises an electron gun to irradiate an electron beam on the one or more contact holes and/or vias wherein the electron beam includes a cross-section which is greater than the one or more contact holes. The system further includes a current measuring device, coupled to the semiconductor wafer, may measure a compensation current, wherein the compensation current is generated in response to the electron beam irradiated on the one or more contact holes. The system also includes a data processor, coupled to the current measuring device, to determine information relating to the one or more contact holes and/or vias using the compensation current.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present invention claims priority from Japanese PatentApplications No. 11-315320 filed Nov. 5, 1999, No. 2000-191817 filedJun. 26, 2000 and No. 2000-311196 filed Oct. 11, 2000, the contents ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a semiconductor device testerusing electron beam and, particularly, to a semiconductor device testerin which current flowing through a semiconductor device irradiated withelectron beam is measured.

[0004] 2. Description of Related Art

[0005] In a semiconductor device such as memory, contact-holes orvia-holes are usually provided for electrically connecting activeelements formed in a lower portion thereof to a wiring layer formed inan upper portion thereof. The contact-holes are formed by etching aninsulating film such as an oxide film from a surface thereof down to anunderlying substrate by reactive ion etching. In order to optimizeetching condition, it is necessary to detect an outer and innerconfigurations of a contact-hole or a state of a bottom of thecontact-hole.

[0006] Since the diameter of contact-hole is in the order of microns orless, visible light can not illuminate the bottom of the contact-hole,so that it is difficult to detect the state of the contact-holeoptically. Therefore, SEM (Scanning Electron Microscope) suitable foranalysis of a fine structure has been mainly used as a tester. In theSEM, a contact-hole region is irradiated with electron beam, which isaccelerated to several tens keV and collimated to several nanometers,and secondary electron produced in the irradiated region is detected bya secondary electron detector, on which an image of the contact-hole isformed. A specimen irradiated with electron beam generates secondaryelectron, an amount of which corresponds to constituting atoms thereof.However, the secondary electron detector in the SEM is usually arrangedin a specific direction, so that a whole of produced secondary electronsis not always detected. If the specimen includes irregularity in itsstructure, there is a case where secondary electron is not detecteddepending upon portions of the specimen, resulting in that contrast isproduced in an image of the specimen under test, which is formed of asingle substance. This is the feature of the SEM.

[0007] On the other hand, an electrical contact is realized through acontact-hole or a through-hole. Therefore, not only a configuration ofan opening portion of the contact-hole but also a configuration and asurface condition of the bottom portion of the contact-hole are veryimportant. In an etching for forming contact-holes each having aspectratio exceeding 10 in concomitant with the recent increase ofintegration density and the number of layers of a semiconductor device,there may be a case where inner diameters of the contact-holes becomedifferent from diameters of opening portions of the contact-holesdepending upon process condition even when the sizes of the openingportions are the same as a designed size. Since such variation of theinner size of the contact-hole substantially affects characteristics ofa semiconductor device, it is necessary for persons in charge of aprocess to control the process such that all contact-holes haveidentical sizes. Further, since such size variation of contact-holesmust not exist in practical products, the products have to be testedtoo. Therefore, a technique capable of non-destructively detecting boththe inner size of the contact-holes and such size variation of thecontact-holes is very important.

[0008] FIGS. 4(a) and 4(b) illustrate a test method using an SEM fortesting a contact-hole 43 having a circular cross section and a resultof the test thereof, respectively, and FIGS. 5(a) and 5(b) illustrate atest method using an SEM for testing a tapered contact-hole and a testresult thereof, respectively. In the test using the SEM, the specimenunder test is scanned by electron beam 31 and secondary electron 32produced in the specimen is detected by a secondary electron detector33.

[0009] It is assumed that the circular contact-hole 43 is formed throughan insulating film 41 such as an oxide film formed on an underlyingsubstrate 42 by etching from an opening portion thereof in a verticaldirection such that the contact-hole 43 has an inner diametersubstantially equal to a diameter of the opening portion, as shown inFIG. 4(a). In such case, energy of secondary electron hardly reaches thedetector 33 unless there is a space large enough to gather a sufficientamount of energy since the energy of secondary electron is small.Therefore, a measured amount of secondary electron becomes as shown inFIG. 4(b). That is, an image of secondary electron obtained becomessuddenly darkened correspondingly to the opening portion of thecontact-hole 43. By this phenomenon, an existence of a contact-hole isdetected.

[0010] On the other hand, it is assumed that a contact-hole 44 has atapered configuration whose diameter is reduced with depth as shown inFIG. 5(a). In such case, secondary electron from the tapered portion ofthe contact-hole may be observed depending upon a position of asecondary electron detector. However, since the aspect ratio of thecontact-hole 44 is large, secondary electron emitted from an inner wallof the contact-hole can not observed practically. Therefore, theconfiguration of the contact-hole 44 and an information of a bottomthereof are not always reflected to a secondary electron image.

[0011] In the tapered contact-hole such as shown in FIG. 5(a), the innerdiameter thereof is reduced with increase of a depth thereof and theremay be a case where a contact resistance of the contact-hole isincreased, resulting in a defective contact-hole even if the diameter ofthe opening portion thereof is acceptable. In the SEM test, however, adetected image becomes dark sharply at the opening portion of thecontact-hole and an information of a bottom thereof is not reflected tothe image regardless of whether the configuration of the contact-hole iscircular or tapered. Thus, it is impossible to distinguish thesecontact-holes by the usual SEM.

[0012] In order to test an interior or a bottom of a contact-hole, amethod of observing a cross section of the contact-hole of a specimenobtained by vertically cutting the specimen along a center axis of thecontact-hole has been employed. This method requires a high leveltechnique for precisely cutting the specimen to two pieces at the centeraxis of the contact-hole. Therefore, in view of the diameter of thecurrent contact-hole in the order of several thousands Å, it ispractically impossible to cut the specimen along the center axis of thecontact-hole with precision of 10% which is necessary to determine thequality of a product. Further, this method is a destructive test andrequires considerable labor and time, in addition to the impossibilityof directly observation of the product.

[0013] In order to solve such problems, JP H10-281746A discloses atechnique in which current produced by electron beam, which is passedthrough a contact-hole and arrived at a substrate, is detected to detecta position and size of a bottom of the contact-hole. Further, JPH4-62857A discloses a technique in which a secondary electron image isobtained by irradiating a contact-hole with not electron beam but ionbeam and measuring a current flowing through a substrate due to the ionbeam irradiation.

[0014] As another prior art, JP H11-026343A discloses a technique inwhich a pattern for measuring a positional deviation of a mask is formedand an amount of positional deviation of the mask is obtained on thebasis of a substrate current produced when electron beam irradiation isperformed. Further, JP P2000-174077A discloses a technique in which anarea containing a plurality of contact-holes is irradiated with electronbeam and a ratio of normal contact-holes in that area is tested on thebasis of current values produced by electron beam passed through thecontact-holes.

[0015] Further, it is possible to know a film thickness by measuring asubstrate current. For example, JP P62-19707A discloses a technique inwhich a relation between a waveform of a substrate current, accelerationvoltage of electron beam and a film thickness, when a pulsed electronbeam irradiation is performed, is preliminarily obtained and a filmthickness is obtained from a current waveform measured by using electronbeam accelerated with a certain acceleration voltage. Further, JPP2000-124276A discloses a technique in which a current, which is not avariation of current wit time but a current value, produced byirradiating a test sample with electron beam and passed through the testsample to a backside surface thereof is measured. In a techniquedisclosed in JP P00-180143A, a current flowing through a thin film to asubstrate, is measured and a film thickness is obtained by comparing themeasured current with a current value obtained for a standard sample andJP P2000-164715A discloses a standard sample suitable for use in thetechnique disclosed in JP P2000-180143A.

SUMMARY OF THE INVENTION

[0016] An object of the present invention is to further improve thetechnique for detecting a substrate current produced by irradiation ofelectron beam to thereby provide a semiconductor device tester capableof non-destructively testing a detailed configuration of a contact-holeand an inner state of a semiconductor device.

[0017] The semiconductor device tester according to the presentinvention, which includes electron beam irradiation means forirradiating a semiconductor device as a sample under test with electronbeam while scanning the semiconductor device, current measuring meansfor measuring current produced in the sample by irradiation of electronbeam and data processing means for processing measured data from thecurrent measuring means, is featured by that the electron beamirradiation means includes collimator means for collimating electronbeam to parallel beam and means for changing acceleration voltage ofelectron beam and the data processing means includes means for obtainingan information related to a structure of the sample in a depth directionon the basis of a difference in transmittivity of electron beam for thesample when the latter is scanned with different acceleration voltages.

[0018] The reason for the use of parallel electron beam in the presentinvention is that, when converging electron beam is used, it isnecessary to condense electron beam to a vertical level of a measuringlocation and, so, it is not suitable in obtaining an information of thesample in a depth direction thereof. When parallel electron beam isused, focal distance becomes infinite so that focus regulation becomesunnecessary.

[0019] The previously described technique disclosed in JP H1-281746A canperform a test for detecting whether or not the contact-hole penetratesthe film. However, it can not provide a detailed information of such asconfiguration of a contact-hole. This is also true for the techniquedisclosed in JP H4-62857A, which uses ion beam. Although there is adescription in JP P2000-124276A of a change of the amount of current oracceleration voltage of electron beam, the purpose of the change ofcurrent or acceleration voltage is to reduce noise, not to check astructure of the test sample in its depth direction. The use of parallelbeam disclosed in JP P2000-174077A is to irradiate the area including aplurality of contact-holes, not to check the structure such asindividual contact-holes of the test sample in the depth directionthereof.

[0020] The electron beam irradiation means includes an electron gun andthe collimator means includes a condenser lens for collimating electronbeam emitted from the electron gun to parallel beam and an apertureplate having an aperture inserted into between the condenser lens andthe semiconductor device, for limiting a spot size of electron beam suchthat electron beam impinges an opening portion. The electron beamirradiation means preferably includes means for moving the sample undertest with respect to electron beam in order to scan the ample withelectron beam.

[0021] Alternatively, the electron beam irradiation means includes anelectron gun and the collimator means may include a first condenser lensfor collimating electron beam emitted from the electron gun to parallelbeam, a second condenser lens arranged such that it constitutes anafocal system, an objective lens and an aperture plate having anaperture and inserted into between the first condenser lens and thesecond condenser lens for limiting a spot size of electron beam. It mayfurther include means for moving the sample under test with respect toelectron beam in order to scan the ample with electron beam.

[0022] The electron beam irradiation means may include means forvertically irradiating the semiconductor device along a line segmentpassing through a center of a measuring region with electron beam havingspot size smaller than an area of the measuring region and the dataprocessing means may include means for obtaining a distance of a bottomof the measuring region from a time between a rising and falling edgesof a current measured along the line segment.

[0023] The data processing means may include area calculation means,which divides a value of current produced in an unknown measuring regionby electron beam irradiation under constant condition by a value ofcurrent produced in a standard sample having a known area of measuringregion by electron beam irradiation under the same constant conditionand obtains an area of the unknown measuring region from a resultingquotient. In this case, the data processing means may include distancecalculation means, which divides the area obtained by the areacalculation means by the ratio (π) of the circumference of a circle toits diameter and obtains a root of the resultant quotient as a distancemeasured from one edge to the other of the unknown measuring region.

[0024] The electron beam irradiation means may include means for settingthe spot size of electron beam to a value large enough to cover all ofthe measuring region in the lump and the data processing means mayinclude means for calculating a ratio of current produced when thestandard sample having the known measuring region area is irradiatedwith electron beam having the large spot size to a value of currentproduced when a measuring region of the unknown sample is irradiatedwith electron beam having the large spot size and means for calculatingan area of the measuring region of the unknown sample from the ratio.

[0025] The data processing means may include means for determining thevalue of current produced when the standard sample is irradiated withelectron beam having known spot size as an amount of current per unitarea of the standard sample.

[0026] The data processing means may further include means for comparinga current measured correspondingly to a positional coordinates if awafer under test irradiated with electron beam with a current to bemeasured at the same positional coordinates of the wafer is good andsetting the kind of process to be performed next on the basis of theresult of the comparison.

[0027] The present invention can be utilized in combination with an SEM.That is, the semiconductor device tester according to the presentinvention further comprises a secondary electron detector for detectingsecondary electron emitted from a surface of a sample under test,wherein the data processing meant may include correspondence means formaking an amount of secondary electron measured by the secondaryelectron detector correspondent with the result of measurement of thecurrent measuring means. In detail, it is possible to verticallyirradiate the sample under test along the line segment passing through acenter of a measuring region with electron beam having spot size smallerthan an area of the measuring region by means of the electron beamirradiating means, obtaining a bottom distance of the measuring regionfrom a distance between a rising and failing edges of current measuredalong the line segment by means of the current measuring means andobtaining an upper distance of the measuring region from a distancebetween a rising and falling edges of the secondary electron detected bythe secondary electron detector. The correspondence means may includemeans for three-dimensionally displaying a circular pillar or a frustumof a cone having the measured bottom distance, upper distance and filmthickness of the measuring region as a bottom diameter, an upperdiameter and a height.

[0028] The semiconductor device tester further comprises tilting meansfor tilting a sample stage on which a sample under test is mounted,wherein the data processing means may include means for processing atilting angle of the sample with respect to electron beam.

[0029] The data processing means may include means for storing a currentvalue corresponding to an electron beam irradiated portion, which isobtained in a location of the sample having no dust, means for comparingthe current value stored in the storing means with a current valuecorresponding to an electron beam irradiated position in the samepattern portion of an unknown sample as that of the sample and means fordetermining existence and size of dust from a difference between arising and falling positions of the current obtained by the comparison.

[0030] The electron beam irradiation means may include means for settinga cross sectional shape of electron beam such that it covers the wholemeasuring region in the lump and at least one end of the cross sectionalshape of electron beam becomes linear and the data processing means mayinclude means for obtaining the distance of the measuring region from adistance between a rising value and a maximum value of current.

[0031] The electron beam irradiation means includes means for setting across sectional shape of electron beam such that it covers a wholemeasuring region in the lump and at least one end of the cross sectionalshape of electron beam becomes linear and the data processing means mayinclude means for calculating a differentiated curve of current withrespect to a distance and means for obtaining a radius of the measuringregion from a distance between a rising position and an apex position ofthe differentiated curve.

[0032] The data processing means may include means for displayingmeasured current values on a map corresponding to the measuredpositions.

[0033] The data processing means may include comparison means forcomparing a measured value obtained in one of two regions on a wafer assamples with a measured value obtained in the other region as areference value and means for extracting a positional coordinates whenthere is a difference equal to or larger than a predetermined constantvalue.

[0034] In this case, the electron beam irradiation means includes meansfor scanning a sample under test with line shaped electron beam havinglength substantially equal to a width of a wiring in a directionperpendicular to a lengthwise direction of the line shaped line andmoving a scan position by a distance equal to the width of the wiringvertically to scanning direction after one line scan is completed andthe comparison means may include means for comparing current waveformsmeasured as variations of current values with respect to electron beamirradiating positions in the two regions.

[0035] The electron beam irradiation means includes means for scanning asample under test with electron beam having size smaller than a minimumwidth of a wiring of the sample in a first direction and moving the scanposition in a direction perpendicular to the scanning direction by adistance corresponding to the width of the wiring every time one linescan is completed and the comparison means may include means forextracting, from current waveforms measured as variations of currentvalues corresponding to electron beam irradiating positions in the tworegions, instantaneous current values at centers of a rising and fallingedges of the current waveform corresponding to the same patternpositions and comparing the instantaneous current values with eachother.

[0036] The electron beam irradiation means includes means for scanning asample under test with line shaped electron beam having a length capableof irradiating a plurality of wiring lines of the sample as a lump in adirection perpendicular to a lengthwise direction of the line shapedelectron beam and moving the sample in a direction perpendicular to thescanning direction by a width of electron beam irradiating a scanposition every time when one line scan is completed and the comparisonmeans may include means for comparing current waveforms measured asvariations of current values for electron beam irradiating positions inthe two regions. In this case, the means for comparing waveforms mayinclude means for integrating the waveforms and comparing the integratedvalues.

[0037] The comparison means may include means for integrating currentfrom a rising edge to a falling edge of one pulse of a current waveformmeasured as a variation of a current from an electron beam irradiatingposition, divider means for dividing the integrated value by a distancebetween the rising edge and the falling edge of the pulse and means forcomparing current values per unit area of the two regions obtained bythe divider means.

[0038] The comparison means may include means for comparing positions ofa rising edge and a falling edge of the pulse of the current waveformmeasured as a variation of current value for an electron beamirradiating position. Alternatively, the comparison means may includemeans for comparing the center position of the rising edge and thefalling edge of that pulse.

[0039] The electron beam irradiation means may include main scan meansfor moving a sample under test with respect to electron beam and subscan means for repeatedly deflecting electron bean in a directiondifferent from a main scan direction simultaneously with the main scan.

[0040] The electron beam irradiation means can switch an operation modebetween a first mode in which individual wiring lines of a sample undertest are irradiated with electron beam and a second mode in which all ofthe wiring lines of the sample are irradiated with electron beam in thelump and the data processing means may include means for analyzing,every constant positional section, spacial frequency of current waveformmeasured as a variation of current value for electron beam irradiatingposition in the first mode and detecting a position in which sectionshaving the same spacial frequency continue for a constant time periodand means for, under an assumption that a plurality of wiring lines arearranged in an array in the detected position, setting the electron beamirradiation means to the second mode and obtaining defect ratio in thelump.

[0041] The means for obtaining information related to the structure inthe dept direction preferably includes means for obtaining athree-dimensional configuration of a through-hole provided in aninsulating film by measuring values of current produced by irradiationof electron beam passing through a portion of the insulating film, whichsurrounds the through-hole, with increased acceleration voltage.

[0042] In order to obtain a three-dimensional configuration of athrough-hole provided in an insulating film, it is necessary to know athickness of the insulating film. The technique disclosed in JPS62-19707A, P2000-124276A or P2000-180143A may be used therefor.

[0043] The semiconductor device tester may further include means fortilting a sample stage on which a sample under test is mounted and themeans for obtaining the three-dimensional configuration preferablyincludes means for detecting whether a diameter of a through-hole isincreased or decreased with depth, from measured values obtained whenelectron beam and an incident angle of electron beam to the sample arechanged.

[0044] The means for obtaining the information related to a structure ina depth direction may include means for detecting deviation of a circuitpattern in an insulating film from measured value of current produced byelectron beam passing through the insulating film.

[0045] Although a technique for measuring a deviation of mask positionis disclosed in JP H11-026343A, the measurement of the mask positiondeviation utilizes a measuring pattern with which a through-hole isprovided when the mask positions are registered. It does not useelectron beam passing through an insulating film.

[0046] The means for detecting deviation of circuit pattern preferablyincludes means for evaluating a deviation of circuit patterns inrespective layers from measured values when penetrating depth ofelectron beam is changed by changing acceleration voltage. In order toobtain a position of the insulating layer in which the circuit patternsoverlap, means for taking in an information related to the circuitpatterns from CAD data is preferably provided.

[0047] In the construction mentioned above, acquisition of currentwaveform is performed by electron beam scanning and measured currentcontains current flowing through a capacitance of a sample dependingupon irradiation frequency or scanning frequency. Therefore, there maybe a case where D.C. current, which can not flow through the sampleessentially, is measured as if it flows through the sample. In order toavoid such phenomenon, the data processing means preferably includesmeans for correcting current component flowing through a capacitance ofa sample under test, which is caused by irradiation frequency ofelectron beam or scanning frequency. In detail, in a case where theelectron beam irradiation means has a construction in which pulsedelectron beam is generated repeatedly, it includes means for changingthe repetition period of electron beam pulse and the correcting meanspreferably includes means for obtaining the D.C. component byextrapolating current value when the sample is continuously irradiatedwith electron beam from current values measured by the current measuringmeans when the sample is irradiated with electron beam with differentrepetition period. The semiconductor device tester may further includemeans for switching scan speed of electron beam from the electron beamirradiation means and the correcting means may include means forobtaining a current value when the scanning speed, which is zero, isextrapolated from the current values measured by the current measuringmeans when the sample is scanned by electron beam at different scanspeeds.

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The above mentioned and other objects, features and advantages ofthe present invention will become more apparent by reference to thefollowing detailed description of the present invention taken inconjunction with the accompanying drawings, in which:

[0049]FIG. 1 is a block diagram of a semiconductor device testeraccording to a first embodiment of the present invention

[0050]FIG. 2 is a block diagram of a semiconductor device testeraccording to a second embodiment of the present invention;

[0051] FIGS. 3(a) and 3(b) show an aperture construction, in which FIG.3(a) shows an aperture for collimating electron beam to beam having acircular cross section and FIG. 3(b) shows an aperture for collimatingelectron beam to beam having a square cross section;

[0052] FIGS. 4(a) and 4(b) illustrate a test of a contact-hole having acircular cross section with using an SEM, in which FIG. 4(a) illustratesa test method and FIG. 4(b) shows an example of a test result;

[0053] FIGS. 5(a) and 5(b) illustrate a test of a tapered contact-holehaving circular cross section with using an SEM, in which FIG. 5(a)illustrates a test method and FIG. 5(b) shows an example of a testresult;

[0054] FIGS. 6(a) and 6(b) illustrate a measuring method of a circularcontact-hole, in which FIG. 6(a) shows a structure of a circularcontact-hole to be measured and FIG. 6(b) shows a measuring systemthereof;

[0055] FIGS. 7(a) and 7(b) illustrate a measuring method of a taperedcontact-hole, in which FIG. 7(a) shows a structure of a circularcontact-hole to be measured and FIG. 7(b) shows a measuring systemthereof;

[0056]FIG. 8 shows a variation of compensation current with respect to abottom area of a contact-hole;

[0057]FIG. 9 shows a variation of compensation current with respect todiameter of a contact-hole;

[0058] FIGS. 10(a) and 10(b) illustrate a measurement using electronbeam of which cross sectional area is larger than the aperture of thehole, in which FIG. 10(a) shows a structure of a contact-hole to bemeasured and a measuring system therefor and FIG. 10(b) shows an exampleof a result of measurement;

[0059] FIGS. 11(a) and 11(b) illustrate a measurement using electronbeam of which cross sectional area is larger than the aperture of thehole, in which FIG. 11(a) shows a structure of a contact-hole to bemeasured and a measuring system therefor and FIG. 11(b) shows an exampleof a result of measurement;

[0060] FIGS. 12(a) and 12(b) illustrate a measurement using electronbeam having cross sectional diameter smaller than a diameter of acontact-hole, in which FIG. 12(a) shows a structure of a contact-hole tobe measured and a measuring system therefor and FIG. 12(b) shows anexample of a result of measurement;

[0061]FIG. 13 is a flowchart of a measurement of a bottom diameter of acontact-hole in a mass-production factory and an example of a qualitydetermination;

[0062] FIGS. 14(a), 14(b) and 14(c) illustrate an example of measurementof a circular contact-hole with using vertical electron beam togetherwith SEM, in which FIG. 14(a) shows a structure of the contact-hole tobe measured and a measuring system therefor, FIG. 14(b) shows an amountof secondary electron measured along a center line of the contact-holeand compensation current, with respect to irradiating position ofelectron beam and FIG. 14(c) shows a restored three-dimensional displayof the contact-hole;

[0063] FIGS. 15(a), 15(b) and 15(c) illustrate an example of measurementof a tapered contact-hole with using vertical electron beam togetherwith SEM, in which FIG. 15(a) shows a structure of the taperedcontact-hole to be measured and a measuring system therefor, FIG. 15(b)shows an amount of secondary electron measured along a center line ofthe tapered contact-hole and compensation current, with respect toirradiating position of electron beam and FIG. 15(c) shows a restoredthree-dimensional display of the tapered contact-hole;

[0064] FIGS. 16(a) and 16(b) illustrate an example of measurement of acircular contact-hole with using slanted electron beam together withSEM, in which FIG. 16(a) shows a structure of the contact-hole to bemeasured and a measuring system thereof and FIG. 16(b) shows an amountof secondary electron measured along a center line of the contact-holeand compensation current, with respect to irradiating position ofelectron beam;

[0065] FIGS. 17(a) and 17(b) illustrate an example of measurement of atapered contact-hole with using slanted electron beam together with SEM,in which FIG. 17(a) shows a structure of the contact-hole to be measuredand a measuring system therefor and FIG. 17(b) shows an amount ofsecondary electron measured along a center line of the contact-hole andcompensation current, with respect to irradiating position of electronbeam;

[0066] FIGS. 18(a), 18(b) and 18(c) illustrate an example of measurementof a reverse-tapered contact-hole with using vertical electron beamtogether with SEM, in which FIG. 18(a) shows a structure of the taperedcontact-hole to be measured and a measuring system therefor, FIG. 18(b)shows an amount of secondary electron measured along a center line ofthe reverse-tapered contact-hole and compensation current, with respectto irradiating position of electron beam and FIG. 18(c) shows a restoredthree-dimensional display of the reverse-tapered contact-hole;

[0067] FIGS. 19(a) and 19(b) illustrate a method for detecting andspecifying an extraordinary thing in a contact-hole, in which FIG. 19(a)shows a structure of the contact-hole to be measured and a measuringsystem therefor and FIG. 19(b) shows an amount of secondary electronmeasured along a center line of the contact-hole and compensationcurrent, with respect to irradiating position of electron beam;

[0068] FIGS. 20(a) and 20(b) illustrate a method for detecting andspecifying an extraordinary thing in a tapered contact-hole, in whichFIG. 20(a) shows a structure of the contact-hole to be measured and ameasuring system therefor and FIG. 20(b) shows an amount of secondaryelectron measured along a center line of the contact-hole andcompensation current, with respect to irradiating position,

[0069] FIGS. 21(a) and 21(b) illustrate a method for detecting andspecifying an extraordinary thing in a reverse-tapered contact-hole, inwhich FIG. 20(a) shows a structure of the contact-hole to be measuredand a measuring system therefor and FIG. 20(b) shows an amount ofsecondary electron measured along a center line of the contact-hole andcompensation current, with respect to irradiating position;

[0070] FIGS. 22(a), 22(b) and 22(c) illustrate an example of measurementof a contact-hole with using electron beam having large cross sectionalarea, in which FIG. 22(a) is a plan view showing a positional relationbetween the contact-hole and electron beam, FIG. 22(b) is a crosssectional view thereof and FIG. 22(c) shows compensation currentobtained with respect to scanning position of electron beam anddifferentiated value thereof;

[0071]FIG. 23 is a flowchart of a measuring method using a combinationof a length measuring mode and a total measuring mode;

[0072]FIG. 24 shows an example of a positional relation between a regionon a wafer to which the length measuring mode is applied and a region onthe same wafer to which the total measuring mode is applied;

[0073]FIG. 25 shows a construction of an apparatus for performing acomparative test by utilizing two test samples;

[0074]FIG. 26 is a flowchart for the comparative test;

[0075] FIG; 27 is a figure for explaining a principle of the comparativetest;

[0076]FIG. 28 shows a portion of FIG. 27 in an enlarged scale;

[0077] FIGS. 29(a) and 29(b) show an example of a result of test, inwhich FIG. 29(a) shows an example of a normal chip and FIG. 29(b) showsa defective chip;

[0078] FIGS. 30(a) and 30(b) show an example of a result of testperformed with using thin electron beam, in which FIG. 30(a) shows anexample of a normal chip and FIG. 30(b) shows a defective chip;

[0079] FIGS. 31(a) and 31(b) show an example of a result of test when aplurality of randomly arranged wiring lines are irradiated with electronbeam having a linear cross section, in which FIG. 31(a) shows an exampleof a normal chip and FIG. 31(b) shows a defective chip;

[0080] FIGS. 32(a) and 32(b) show an example of a result of test whenwiring lines have identical configurations in longitudinal directions,in which FIG. 32(a) shows an example of a normal chip and FIG. 32(b)shows a defective chip;

[0081] FIGS. 33(a) and 33(b) show an example of a result of test whenwiring lines having different width exist in axis-symmetry, in whichFIG. 33(a) shows an example of a normal chip and FIG. 33(b) shows adefective chip;

[0082] FIGS. 34(a) and 34(b) show an example of a result of test whenwiring lines having different widths exist randomly, in which FIG. 34(a)shows an example of a normal chip and FIG. 34(b) shows a defective chip;

[0083]FIG. 35 shows a construction of an apparatus for performing acomparative test by comparing integrated values of current waveforms;

[0084]FIG. 36 shows a flowchart of the apparatus shown in FIG. 35;

[0085]FIG. 37 shows a construction of an apparatus for performing acomparative test on the basis of current value per unit area;

[0086]FIG. 38 shows a flowchart of the apparatus shown in FIG. 37;

[0087] FIGS. 39(a) and 39(b) show a relation between wiring coverage ofelectron beam and current waveform, in which FIG. 39(a) shows an examplewhen the coverage is 100% and FIG. 39(b) shows an example when thecoverage is 50%;

[0088]FIG. 40 shows a construction of an apparatus for performing acomparative test by using a plurality of chips on a common substrate;

[0089]FIG. 41 shows a flowchart of the apparatus shown in FIG. 40;

[0090]FIG. 42 is a flowchart of a test in which quality of wiring isdetermined by a rising and a falling edges of current waveform;

[0091] FIGS. 43(a) and 43(b) show a test result, in which FIG. 43(a)shows a normal wiring and FIG. 43(b) shows defective wiring;

[0092]FIG. 44 is a flowchart of a test in which quality of wiring isdetermined by a center position of a rising and a falling edges ofcurrent waveform;

[0093]FIG. 45 shows a construction of an apparatus for performingelectron beam sub scan;

[0094]FIG. 46 shows an example of scan locus;

[0095]FIG. 47 shows a test flowchart with which a test speed of an arrayregion is increased;

[0096]FIG. 48 shows an example of a power spectrum obtained by afrequency analysis;

[0097]FIG. 49 illustrates a measurement of a three-dimensionalconfiguration of a contact-hole;

[0098]FIG. 50 illustrates a measurement of a three-dimensionalconfiguration of a contact-hole;

[0099]FIG. 51 illustrates a measurement of a three-dimensionalconfiguration of a contact-hole;

[0100]FIG. 52 illustrates a measurement of a three-dimensionalconfiguration of a contact-hole;

[0101]FIG. 53 illustrates a measurement of a three-dimensionalconfiguration of a contact-hole;

[0102]FIG. 54 illustrates a measurement of a three-dimensionalconfiguration of a contact-hole;

[0103]FIG. 55 shows a process flowchart for obtaining athree-dimensional configuration of a contact-hole bysuccessive-approximation;

[0104]FIG. 56 illustrates a portion of the process;

[0105]FIG. 57 illustrates another portion of the process;

[0106]FIG. 58 illustrates another portion of the process;

[0107] FIGS. 59(a) and 59(b) illustrate an evaluation example ofinterlayer deviation, in which FIG. 59(a) is a cross section of a deviceand FIG. 59(b) shows a result of measurement;

[0108] FIGS. 60(a) and 60(b) illustrate another evaluation example ofinterlayer deviation in which FIG. 60(a) is a cross section of a devicewith no deviation and FIG. 60(b) shows a result of measurement;

[0109] FIGS. 61(a) and 61(b) illustrate another evaluation example on asimilar device with that of FIGS. 60(a) and 60(b), in which FIG. 61(a)is a cross section of the device and FIG. 61(b) shows a result ofmeasurement;

[0110] FIGS. 62(a) and 62(b) illustrate an another evaluation example ofinterlayer deviation, in which FIG. 62(a) is a cross section of a deviceand FIG. 62(b) shows a result of measurement;

[0111]FIG. 63 is a flowchart of measurement when a main insulating filmis formed of one kind of material;

[0112]FIG. 64 shows an example of compensation current with respect tofilm thickness;

[0113]FIG. 65 shows an example of compensation current with respect toacceleration voltage;

[0114]FIG. 66 is a flowchart of measurement when there are a pluralityof insulating films;

[0115]FIG. 67 is a flowchart of deviation determination after images ofrespective layers are obtained;

[0116]FIG. 68 is a flowchart of measurement for acquiring an informationof a plurality of layers together;

[0117]FIG. 69 shows an example of process flowchart for backgroundcorrection; and

[0118]FIG. 70 shows another example of process flowchart for backgroundcorrection.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0119] The present invention will be described in detail with referenceto the drawings. In the drawings, same or similar components aredepicted by same reference numerals, respectively, with detaileddescription thereof being omitted.

[0120] Generation of Parallel Electron Beam

[0121]FIG. 1 is a block diagram showing a construction of asemiconductor device tester according to a first embodiment of thepresent invention. The semiconductor device tester includes an electrongun 1 for generating electron beam 2, a condenser lens 3 and an apertureplate 4, which collimates the electron beam 2, a movable stage 6 forscanning irradiating positions of a sample 5 with electron beam bymoving the sample 5, an electrode 7 and an ammeter 9, which measurescurrent produced in the sample 5 by irradiation of electron beam 2, amoving distance measuring device 8 for measuring a moving distance ofthe movable stage 6, a data processor 10 such as a computer processingdata resulting from the ammeter 9 and a beam control portion 11 forperforming controls such as change of acceleration voltage of electronbeam and/or change of irradiation period.

[0122] Electron beam 2 emitted from the electron gun 1 is oncecollimated to parallel beam by the condenser lens 3 and directed to theaperture plate 4 having very small aperture. The aperture plate 4 ismade of such as metal and is grounded such that electron irradiating theaperture plate 4 is not accumulated therein. Electron beam 2 passedthrough the small aperture of the aperture plate 4 becomes very thinbeam having cross sectional area substantially equal to an area of theaperture and fallen in the sample 5. In order to prevent the diameter ofthe aperture from being changed by thermal expansion of the apertureplate 4, the aperture plate 4 may be cooled suitably.

[0123] FIGS. 3(a) and 3(b) show examples of a construction of theaperture plate including an aperture and a shielding portion, in whichFIG. 3(a) shows an aperture 21 provided in a center portion of theaperture plate formed of an electron beam shielding material forcollimating the cross section of electron beam to circular and FIG. 3(b)shows an aperture 21 for collimating the cross section of electron beamto square. Each of the apertures 21 is surrounded by a shielding portion22. The shielding portion 22 of the aperture plate 4 is formed oftungsten, molybdenum, silicon, polysilicon, gold, palladium or titanium,etc., which, when irradiated with electron beam, hardly generates gas. Adiameter of the aperture 21 is in a range from several hundreds Å to1000 Å when a distance is to be obtained by scanning an interior of acontact-hole or several microns when a whole single contact-hole isirradiated with electron beam at one time. The shape of the aperture 21is not limited to square or circular. A rectangular, ellipsoidal orother polygonal aperture may be used.

[0124] The cross sectional area of electron beam may be larger orsmaller than the area of the aperture 21. When the cross sectional areaof electron beam is smaller than that of the aperture 21, it is possibleto obtain a similar result to that obtainable when electron beam havingcross sectional area larger than that of the aperture 21, by scanningthe aperture 21 therewith.

[0125] The sample 5 is mounted on the electrode 7, which is mounted onthe movable stage 6. The moving distance measuring device 8 formeasuring the moving distance of the movable stage 6 precisely inangstrom order according to the principle of an interferometer isprovided in the vicinity of the movable stage 6. Although an opticalsystem is usually used as the moving distance measuring device 8, it ispossible to use other system for detecting a physical amount which ischanged with distance, such as a system utilizing electromagnetic wave,electric resistance or capacitance or a system utilizing aquantum-mechanical effect.

[0126] The sample 5 may be in contact with the electrode 7 so that itcan contact with the electrode in D.C. sense or, when electron beamirradiating the sample 5 is high frequency-modulated, the sample 5 maybe arranged adjacent to the electrode 7 since current can be measured byan capacitive coupling. In general, in the fabrication method ofsemiconductor device, a local oxide film for element separation isformed on a rear surface of a substrate. Therefore, an insulating filmis usually formed on the rear surface of the substrate. When the sample5 is such wafer, it may be effective to use a capacitive coupling stagein order to realize an electric contact between the sample 5 and thestage 6. Alternatively, it may be possible to provide an electricalconnection by utilizing side faces of the wafer.

[0127] Since size of the contact-hole to be measured is very small, thesample 5 should be put on the stage 6 in flat. In order to realize sucharrangement of the sample 5 on the stage 6, it may be effective to pressan outer periphery of the ample 5 onto the stage 6 by using such asring-shaped jig.

[0128] Current collected by the electrode is measured by the ammeter 9.The measured current is converted into a digital signal and outputted tothe data processor 10. In order to improve the anti-noisecharacteristics of the tester, it may be effective to construct theammeter 9 with a differential amplifier.

[0129] The data processor 10 processes various data and, particularly,can obtain an information related to a structure of a sample under testin a depth direction thereof from a difference of transmittivity ofelectron beam of the sample when scanned with electron beam at differentacceleration voltages.

[0130]FIG. 2 is a block diagram of a semiconductor device testeraccording to a second embodiment of the present invention, which issuitable when a cross sectional area of electron beam is in micronorder. In this tester, an electron beam generation system includes anafocal system composed of a second condenser lens 15 and an objectivelens 16 and constitutes an electron optics system for convertingincident parallel beam into parallel beam having cross sectional areasmaller than an aperture area of an aperture plate 14.

[0131] That is, electron beam 12 emitted from the electron gun 1 isconverted into parallel beam by the first condenser lens 13 and, then,converted into thin parallel beam by the aperture plate 14. Thereafter,the thin parallel beam is converged by the second condenser lens 15 anddirected to the objective lens 16. In this electron beam generatingsystem, the final beam, which is used to irradiate the sample 5, isformed without using the aperture of the aperture plate. Therefore, itis possible to easily form very thin electron beam having crosssectional area in the order of 100 Å, which is difficult to realize withan aperture by directly machining the aperture plate. By scanning a widearea by such thin electron beam, it is possible to provide a similareffect to that obtainable when the sample is totally irradiated withthick electron beam.

[0132] When a secondary electron detector is added to the semiconductordevice tester shown in FIG. 1 or 2, it can be utilized in an SEM shownin FIG. 4(a) or FIG. 5(a).

[0133] Now, a contact-hole, which is to be tested in this invention,will be described. The contact-hole is formed in an oxide film or adielectric film formed on an underlying substrate such as a siliconsubstrate such that it extends from a surface of the oxide film or thedielectric film down to a surface of the substrate. In a normalcontact-hole, the surface of the substrate or a surface of a wiringlayer formed thereon is in an exposed state.

[0134] The contact-hole is formed by applying reactive ion etching withusing fluorine containing gas as an etchant to an oxide film on which aresist having an opening is provided. The contact-hole currently usedmainly has a very thin structure having aspect ratio of 10 or more, thatis, a diameter of the contact-hole with respect to a thickness of theoxide film, which is usually several microns thick, is 0.15 microns. Thereactive ion etching is a physicochemical etching. Practical etchingspeed depends upon an etching speed of the oxide film by ions offlourine containing gas supplied vertically to the surface of thesubstrate at high speed and a forming speed of a high molecularfluorocarbon film produced by the etching in general, the etchingreaction of the oxide film inside the contact-hole, to which ions offluorine containing gas impinge, is enhanced and a high molecularfluorocarbon film is deposited on the sidewall of the contact-holeformed by the same etching reaction. Since the sidewall of thecontact-hole is protected by this mechanism, it becomes possible to forma very deep vertical hole. On the other hand, when the etchingprogresses and the contact-hole reaches the underlying substrate, theoxide film etching reaction is changed to a reaction for etching a highmolecular film, since there is no oxygen in the substrate. Therefore,the progress of etching into the underlying substrate is automaticallyterminated.

[0135] Since, however, a balance of these reactions is sophisticated,there may be a case where the etching of the oxide film is suddenlystopped before the contact-hole reaches the underlying substrate orwhere the underlying substrate is etched, by variation of sophisticatedcondition of the fabrication equipment. Since such phenomenon causes adefective contact-hole or through-hole to be formed, such defect must bedetected.

[0136] Measurement of Bottom Diameter of Contact-Hole

[0137] A technique for measuring a bottom diameter of such contact-holewill be described.

[0138] FIGS. 6(a) and 6(b) illustrate the measuring method, in whichFIG. 6(a) shows a structure of a contact-hole 43 to be measured and ameasuring system therefor and FIG. 6(b) shows an example of a result ofmeasurement. The contact-hole 43 is formed such that it penetrates an minsulating film 41 formed on an underlying substrate 42. The insulatingfilm 41 may be an oxide film or a nitride film, etc. In a good, that is,normal contact-hole, a surface of the underlying substrate 42 or asurface of a wiring layer formed below the insulating film is exposed.Electron beam 31 having a diameter in the order of 100 Å and generatedby the tester shown in FIG. 1 or 2 is vertically directed to a samplehaving the contact-hole 43 formed therein while scanning ithorizontally. Acceleration voltage and current of electron beam 31 areset to in a range from 0.5 kV to several kV and several nA,respectively. When electron beam 31 passes through the contact-hole 43down to the underlying substrate 42, current flows through theunderlying substrate 42. The current is referred to as “compensationcurrent”. FIG. 6(b) shows compensation current produced when the sampleis scanned by electron beam in a horizontal direction along a centerline of the contact-hole 43.

[0139] Since electron beam has a finite cross sectional area, thecompensation current starts to rise at a time when electron beam crossesan edge portion of the insulating film and saturates when electron beamcompletely reaches a bottom of the contact-hole, as shown in FIG. 6(b).When electron beam exists from the bottom portion of the contact-hole,compensation current starts to decrease from the saturated value andbecomes zero when electron beam completely leaves the contact-hole.

[0140] Since the cross section of the contact-hole is usually circular,a distance characterizing the contact-hole is a diameter or radius ofthe circle defining the bottom portion of the contact-hole. In order toobtain the diameter or radius of the contact-hole, it is necessary toperform the measurement along a line passing through a center of thecontact-hole. This can be done by exactly obtaining a position to beirradiated with electron beam from a secondary electron image or CADdata, which is a design information, and controlling a position controlmotor of the wafer stage or controlling electron beam by means of adeflector such that the electron beam irradiated position moves alongthe center line of the contact-hole.

[0141] The compensation current shown on an ordinate in FIG. 6(b)depends upon the thickness of the oxide film on the bottom portion ofthe contact-hole. That is, the compensation current in a region of athick oxide film such as sidewall of the contact-hole becomessubstantially zero, while large compensation current is observed in aregion in which underlying silicon or underlying wiring layer isexposed. Therefore, the compensation current observed along the centerline of the contact-hole is zero outside the region of the contact-holeand becomes a certain value larger than zero in the region in whichsilicon is exposed. Since the region in which the compensation currentis not zero corresponds to the region in which the bottom portion of thecontact-hole is exposed, a width within which silicon is exposed isobtained by measuring the distance. Therefore, the measured distancecorresponds to the diameter of the bottom portion of the contact-hole.

[0142] FIGS. 7(a) and 7(b) illustrate a measurement of a taperedcontact-hole, in which FIG. 7(a) shows a structure of a contact-hole tobe measured and a measuring system therefor and FIG. 7(b) shows anexample of a result of measurement. A diameter of the taperedcontact-hole 44 to be measured reduces from that of an opening portionthereof with depth thereof. A taper angle is relatively large andthickness of an insulating film 41 exceeds 1000 Å immediately when aposition irradiated with electron beam is shifted only slightly from abottom of the contact-hole. In a region in which the apparent thicknessof the insulating film 41 is large, there is substantially nocompensation current produced. Since the compensation current isproduced in a region in which the bottom of the contact-hole is exposedand substantially no current is produced otherwise, a distance alongwhich the compensation current is observed corresponds to a diameter ofthe bottom of the contact-hole. As such, even when the contact-hole istapered, it is possible to measure the distance of the bottom of thecontact-hole even when the contact-hole is tapered.

[0143] Incidentally, since the cross sectional diameter of electron beamis finite, the waveform of compensation current has a rising portion anda falling portion. Therefore, the diameter of the contact-hole can beobtained from various positional information contained in the waveformof compensation current such as rising position, falling position or aposition at which the current is returned to zero from a position atwhich the current completely saturates, etc.

[0144] Depending upon the acceleration voltage of the electron beam,there may be a case where the compensation current flows even if thebottom portion of the contact-hole is not irradiated with electron beamif the taper angle is not large. By utilizing this phenomenon andrepeating the measurement while changing the acceleration voltage, it ispossible to obtain a three-dimensional structure of the contact-hole, asto be described in detail later.

[0145]FIG. 8 shows a variation of compensation current observed when abottom area of a contact-hole is changed under condition in which awhole bottom portion of the contact-hole is irradiated with uniformelectron beam. As shown in FIG. 8, it is clear that the compensationcurrent is proportional to the bottom area of the contact-hole.

[0146]FIG. 9 shows a variation of compensation current corresponding toa diameter (converted bottom diameter of contact-hole) of a circularbottom area of the contact-hole. Since the area is proportional tosquare of the diameter of the bottom of the contact-hole, thecompensation current becomes proportional to the square of the bottomdiameter.

[0147] FIGS. 10(a) and 10(b) illustrate a measurement of a contact-holeby using electron beam of which cross sectional area is larger than theaperture of the hole, in which FIG, 10(a) shows a structure of acontact-hole to be measured and a measuring system therefor and FIG.10(b) shows an example of a result of measurement. FIGS. 11(a) and 11(b)illustrate a measurement of a tapered contact-hole by using electronbeam of which cross section area is larger than the aperture of thehole, in which FIG. 11(a) shows a structure of the contact-hole to bemeasured and a measuring system and FIG. 11(b) shows an example of aresult of measurement. In each of the measurements, the electron beamgenerator shown in FIG. 1 or 2 is used and a cross sectional area of theelectron beam is set to a value (for example, several microns square)larger enough than an area of the contact-hole. Compensation current ismeasured under condition that a sample is vertically irradiated withelectron beam such that a whole bottom of the contact-hole thereof isirradiated simultaneously with the electron beam. An electron beamsource is preferably capable of emitting electron beam whose intensitydistribution within a cross sectional beam area is as flat as 1% orless.

[0148] When a whole contact-hole 43 or 44 is irradiated with electronbeam 51 at once, compensation current produced in an exposed portion ofan underlying substrate 42 is measured by an ammeter 9 at once. Sincethe secondary electron emitting efficiency is specific to substance tobe irradiated with electron beam, an amount of compensation current inunit area of the region in which the underlying layer is exposed isconstant throughout the region if electron beam irradiation condition isthe same. Therefore, when the whole bottom of the contact-hole 43 or 44is irradiated with electron beam 51, compensation current, which isproportional to the bottom area of the contact-hole 43 or 44, isobserved as shown in FIG. 10(b) or 11(b).

[0149] Utilization of Standard Sample

[0150] The compensation current thus obtained may be changed delicatelyupon measuring condition. Therefore, the compensation current isconverted into an area of a contact-hole by using a standard value ofcompensation current obtainable when a state of a sample is known. Thatis, a compensation current per unit area of a standard sample having acontact-hole, a bottom area of which is known, is preliminarily measuredunder certain electron beam irradiating condition and, then, an amountof compensation current for a sample having a contact-hole, bottom areaof which is unknown, is obtained by irradiating it with similar electronbeam. The amount of compensation current obtained for the unknown sampleis divided by the compensation current of the standard sample to obtaina ratio of the bottom area of the contact-hole of the sample under testto the bottom area of the contact-hole of the standard sample. Thisprocedure is based on an assumption that an amount of compensationcurrent per unit bottom area of the contact-hole of the standard sampleis equal to an amount of compensation current per unit bottom area ofthe contact-hole of the sample under test.

[0151] FIGS. 12(a) and 12(b) illustrate a similar measurement of abottom of a contact-hole by using electron beam having cross sectionaldiameter smaller than a diameter of the contact-hole, in which FIG.12(a) shows a structure of the contact-hole to be measured and ameasuring system and FIG. 12(b) shows an example of a result ofmeasurement. When the cross sectional area of electron beam is smallerthan that of the contact-hole, compensation current is obtained in onlya position irradiated with electron beam. However, by integrating valuesof current produced by scanning a whole area of the contact-hole to betested, it is possible to obtain the diameter of the contact-holeaccording to a similar procedure to that used to obtain the totalcompensation current. In a case where time constant of the ammeter islarge, the integrated value of current becomes substantiallyproportional to the average current value. Therefore, it is possible toestimate a diameter of the contact-hole by using the average currentvalue indicated on the ammeter.

[0152] In a case where the tilting angle of a sidewall of the taperedcontact-hole is small, compensation current flows naturally even when abottom of the contact-hole is not irradiated with electron beam sincethe thickness of the insulating film becomes small. The condition underwhich the above method can be simply applied can be determined bythickness of the insulating film, power of electron beam and taper angleof the contact-hole, etc.

[0153] Since compensation current per unit area depends upon materialexposed in the bottom of the contact-hole, acceleration voltage ofelectron beam and/or injected current. It is necessary to obtain arelation between compensation current and area by performing requiredpreliminary experiments and to convert the relation into a table or afunction when the measurement is performed with using other material orother condition.

[0154] Example of Measurement of Bottom Diameter of Contact-Hole

[0155] The inventors have calculated the bottom diameter of thecontact-hole by using a sample made on an experimental basis and haveverified the calculation. In the experiment, a contact-hole having acircular cross section such as shown in FIG. 10(a) was preliminarilyfabricated as a standard sample. A diameter of an opening portion of thecontact-hole and a diameter of a bottom portion of the contact-hole were0.1 micron, respectively, a material exposed on the bottom of thecontact-hole was silicon, an insulating film, which becomes a sidewallof the contact-hole, was a silicon oxide film. When electron beam wasdirected with acceleration voltage of 1 kV, compensation current of 100pA was observed. Then, compensation current for a contact-hole such asshown in FIG. 11(a) having the same opening diameter as that of thestandard contact-hole and an unknown bottom diameter was measured undera similar condition. Compensation current of about 50 pA was observedfor the unknown sample, from which it was confirmed that the bottom areaof the unknown contact-hole is 50% of that of the standard contact-hole.

[0156] On the other hand, the configuration of a practical contact-holecan be investigated by the cross sectional configuration test(destructive test) of SEM. By obtaining a correspondence between thediameter of the contact-hole of the standard sample, which is obtainedfrom the cross sectional area, and the compensation current thereof, itis possible to obtain the bottom area of the contact-hole from themeasured compensation current of the unknown sample. Further, assumingthat the shape of the bottom of the contact-hole of the unknown sampleis analogous to that of the standard sample regardless of its diameter,the diameter of the contact-hole to be measured can be obtained by aroot of the area.

[0157] In the above described experiment, the diameter of thecontact-hole of the unknown sample was 0.07 microns.

[0158] The number of scans of a contact-hole with electron beam.However, in order to improve the preciseness of measurement, it ispossible to scan the same position several times. In such case, it ispossible to calculate a diameter of contact-hole from an average valueof compensation current obtained when a certain test region is scannedseveral times.

[0159] Determination of Compensation Current per Unit Area when BottomArea is Unknown

[0160] A method for determining compensation current per unit area whenthe standard sample having a contact-hole whose bottom area is known cannot be prepared will be described with reference to FIGS. 12(a) and12(b). In the method, electron beam 52, which is sufficiently thinnerthan an opening area of a contact-hole of a sample and has a known spotsize, is vertically directed into the contact-hole. Since the spot sizeof electron beam produced by the tester shown in FIG. 1 or 2 isrestricted by size of the aperture forming in the aperture plate, it ispossible to obtain the size of the electron beam by calculation. Inorder to further improve the accuracy of measurement, the diameter ofelectron beam is directly obtained by the knife edge method, etc. Whensuch electron beam is directed to a standard contact-hole, compensationcurrent such as shown in FIG. 12(b) is measured. A compensation currentper unit area of the standard contact-hole is obtained by dividing thethus obtained compensation current by the spot size of electron beam.

[0161] Utilization in Mass-Production Factory

[0162]FIG. 13 shows a flowchart in a case where the above describebottom diameter measurement of contact-hole is utilized in amass-production factory and a table showing an example of good or baddetermination.

[0163] The size of contact-hole is one of factors which determine theamount of current flowing through the contact-hole. In a high speedmemory or a logic device, very high speed pulse signals operate withsophisticated timing. Since a size variation of contact-hole changes atime constant of a circuit through a contact resistance thereof, thepulse transmission time becomes different from a designed value, causingan operation of the circuit to be defective. Therefore, when there is asize variation of contact-holes, which exceeds a certain range, itaffects a related circuit adversely even if an electric connection isestablished. In order to prevent such defect from occurring, it isnecessary in a mass-production factory to severely manage a variation ofbottom diameters of contact-holes to be fabricated.

[0164] It is assumed, for example, that a contact-hole having bottomdiameter of 0.1 micron is formed with fabrication tolerance of ±0.01micron (±10%). The bottom diameter tolerance of 10% is equivalent to aconverted area tolerance of ±20%. The bottom size of contact-hole ismanaged on the basis of this reference according to the flowchart shownin FIG. 13.

[0165] First, compensation current of each of contact-holes existing ina wafer is measured by using electron beam (S1). A result of themeasurement is stored in a memory or a magnetic disk. The recordingmedium is not limited thereto and may be any other medium provided thatit can record the result of measurement. Then, a standard compensationcurrent obtained by a normal contact-hole is compared with the measuredand recorded compensation current (S2). If a difference of the recordedcompensation current from the standard compensation current is within±20%, the measured contact-hole is decided as a normal contact-hole andan information indicating that the measured contact-hole is normal isrecorded in the memory. A table in FIG. 13 shows an example of resultsof decision obtained for contact-holes positioned in X-Y coordinates(1, 1) . . . (1, 5) with measured bottom diameters and quality decisionsthereof (S3). When the number of defective contact-holes is smaller thana certain reference value (S4), the wafer is put on a wafer carrier fortransportation to a next step (S5). On the other hand, when the numberof defective contact-holes exceeds the reference value, the wafer itselfis decoded as defective. In such case, the succeeding process for thewafer is stopped and the wafer in question is put on a carrier todiscard it (S6). In this case, an instruction for regulating an etchingapparatus, etc., is sent to the factory side.

[0166] For the measured values of bottom diameters of the respectivecontact-holes, a statistical value thereof, such as dispersion oraverage, etc., of the measured values, is calculated and compared with astatistical value of the normal contact-holes. Since a result of suchcomparison can be analyzed before defective electric connection ofcontact-hole occurs practically, it is possible to precisely knowfluctuation and/or tendency of the process change. Further, since it ispossible to find defective wafer quickly, it is possible to know causesfrom which the wafer becomes defective to thereby prevent occurrence ofsubsequent defective products.

[0167] In a recent semiconductor integrated circuit device, the scale ofcircuit is very large and the number of contact-holes is being increasedin geometric progression. In such circuit device, it is difficult tomeasure all of the contact-holes in a wafer. On the other hand, aplurality of identical chips are regularly arranged on the wafer. It ispossible to determine the quality of the chips by interlace-scanningidentical positions of the respective chips. In such case, it is alsopossible to measure, in the lump, bottom diameters of a plurality ofcontact-holes in the positions of the respective chips to be scanned toobtain an average bottom diameter. In the case where the average bottomdiameter of a plurality of contact-holes is to be obtained, it ispossible to use a single thick electron beam collimated by the apertureto irradiate the contact-holes or scan the contact-holes with thinelectron beam in the jump. When the single thick electron beam is usedto irradiate the contact-holes in the lump, it may be possible to obtainan average value by irradiating the contact-holes with electron beam aplurality of times. Similarly, the number of electron beam scans may beone or a plurality of times.

[0168] Map Display

[0169] Further, it is possible to map results of measurement ofcompensation current of a wafer or diameter of a contact-hole, etc.,correspondingly to positions at which the measurement is performed. Forexample, it is possible to know a distribution of diameters of thecontact-holes in the wafer by mapping the compensation current values orthe diameters of the contact-holes as a contour line. The contour mapdisplay can be performed by storing the compensation current informationand the position information thus obtained and displaying them on animage display device or a recording sheet, etc.

[0170] When the information is displayed on the image display devicewith using the compensation current value or the diameter of the openingportion of the contact-hole as a reference, there may be a case whereluminance is too high or too low, causing an image on a screen to behardly looked. Therefore, it is necessary to correct the image displayto thereby make the displayed image easily visible. As a correctionmethod of the image display, a regulation of luminance on the basis of acenter value may be considered, for example. Further, since defectiveproducts is more important than good products in fabrication process, itis preferable to make an information of defective product easier tolook.

[0171] Quality Determination by Map Display and Process Evaluation

[0172] The quality of contact-hole can be classified on the basis ofcompensation current, diameter of contact-hole or configuration ofcontact-hole. By classifying every wafer or every plural wafers on thebasis of identical etching condition identical processing device oridentical processing device used in the preceding step, variousinformation can be acquired. These classification data are preferablydisplayed by a method similar to the contour display. In such case, itis possible not only to determine the quality of wafer but also to knowan etching distribution or other processing state of an etching device,so that it becomes easy to early detect a failure of the processingmachine and optimize the processing condition by such as averaging theetching rate of the etching machine.

[0173] For example, the contact-hole is usually formed by dry-etchingand the etching machine therefor is regulated such that the etching ratebecomes equal for a whole area of the machine. Nevertheless, the wholesurface includes locations in which etching rate is high and locationsin which etching rate is low, inevitably. Comparing contour linedisplays of results of measurement of contact-holes of a plurality ofwafers, the tendency of total etching rate distribution of the etchingmachine is known. Therefore, it is possible to improve the evenness ofetching rate of the etching machine by regulating the machine, forexample, changing a tilting angle of the electrode thereof, such thatthe total etching rate distribution is corrected.

[0174] There may be various methods for acquiring the etching ratedistribution of a plurality of wafers. For example, the distribution maybe obtained by collecting only wafers etched under identical workingcondition or standardizing wafers etched under different conditions.

[0175] One reason for existence of the etching rate distribution is athickness distribution of an insulating film formed prior to the etchingstep. The thickness distribution of the insulating film may be due to astate of CVD device. In such case, it is possible to investigate a causeof defective product by collecting data of wafers, whose etching step isperformed by using the same machine as that used in a precedingfabrication. By using such data, it becomes possible to specify aproblem of the preceding step from the measurement of diameter ofcontact-hole, with which the etching quality is determined.

[0176] In a case where the tendency of the etching machine is known, itis possible to shorten a time required for the measurement, by testingnot a whole surface of a wafer but only locations of the surface inwhich defect tends to occur. For example, it may be possible to measureonly portions of the wafer at which the etching rate is high (largecompensation current and large opening diameter) or low (smallcompensation current and small opening diameter).

[0177] From the diameter distribution of contact-holes, otherinformation than that mentioned above, which is valuable in newlystarting up the etching machine, regulating the etching machine afteroverhaul and/or confirming repair performed for the etching machine, isobtained and it becomes possible to complete the works such as start-upand regulation of the etching machine within a short time by supplyingdata necessary for these works from the information. Further, thediameter distribution of contact-hole is also used as a maintenanceinformation of the etching machine. For example, it is possible toperform a precise estimation of an overhaul timing by statisticallymonitoring deviation of a defective contact-hole distribution from agood contact-hole distribution and increase of defective contact-holes,etc., or using it in an extraordinary substance test to be describedlater. Further, there is another effect that an abnormality of theetching machine can be detected before the abnormality occurs.

[0178] In the usual fabrication of semiconductor wafer, the batch systemis employed. That is, a plurality of wafers are fabricated as a batch ineach fabrication step. Therefore, the quality determination of wafer maybe done for only a first wafer and a last wafer in the batch. When it isconfirmed that the first wafer becomes defective in a certainfabrication step, all of wafers succeeding the first wafer may be testedand, at a time when a defect is detected, the fabrication machine usedin that step may be regulated or may be regulated on the basis of themeasurement result of the first wafer.

[0179] Linkage with SEM

[0180] Since the contact-hole has a three-dimensional structure, it isvery preferable to obtain a test result which can clearly show a featureof the tree-dimensional contact-hole. Although a method for obtaining anexact three-dimensional structure of the contact-hole will be describedin detail later, the method will be described briefly here.

[0181] In the method to be described briefly, a diameter α of an openingportion of a contact-hole, which has a circular cross section usually, adiameter β of a bottom portion of the contact-hole and a depth d thereofare specified and a configuration of the contact-hole is roughlyrepresented. That is, an information of a shape or material of thebottom of the contact-hole obtained from the compensation currentmeasured and a shape of the opening portion of the contact-hole obtainedfrom a usual scanning electron image are synthesized. The materialinformation is estimated from an amount of compensation current measuredby some acceleration voltages according to the nature that compensationcurrent depends upon an underlying material. The depth of thecontact-hole is obtained by an electron beam measurement to be describedlater. However, it may be obtained by using a thickness of theinsulating film in which the contact-hole is formed, practicallymeasured when it is formed.

[0182] FIGS. 14(a), 14(b) and 14(c) and 15(a) and 15(b) illustrate themeasuring method of a contact-hole having a circular cross section and acontact-hole having a tapered contact-hole, respectively, in which FIGS.14(a) and 15(a) show structures of the circular and taperedcontact-holes, respectively, FIGS. 14(b) and 15(b) show relations ofsecondary electron and compensation current measured along a center lineof the contact-hole to electron beam irradiation position and FIGS.14(c) and 15(c) show three-dimensional displays of restoredcontact-holes, respectively. For simplicity of description, it isassumed that the contact-hole is scanned once along the center linethereof.

[0183] As electron beam scanning a periphery of the contact-hole and aninterior thereof, the parallel electron beam obtained by the testershown in FIG. 1 or 2 is utilized. When converging electron beam is used,it is necessary to regulate a focus of the beam to a vertical positionwhich is different between a case where the periphery of thecontact-hole is scanned and a case where the bottom of the contact-holeis scanned. However, when the parallel electron beam is used, the focallength becomes infinite and, therefore, there is no need of focusregulation.

[0184] The diameter α of the opening portion of the contact-hole 43shown in FIG. 14(a) is substantially the same as the diameter β of thebottom thereof. In this case, the rising and falling positions of theamount of secondary electron and the compensation current are coincidentas shown in FIG. 14(b). The three-dimensional configuration of thecontact-hole having circular cross section shown in FIG. 14(c) isobtained from the result of measurement and the depth d of thecontact-hole, which is obtained from the process data. Further, it ispossible to obtain a more precise three-dimensional display by measuringa plurality of cross sectional configurations while changing the scandirection such that it passes the center of the contact-hole. Thereduction of cross sectional configuration to a three-dimensional imagemay be performed by various methods, which are used in the field ofthree-dimensional computer graphics.

[0185] The diameter α of the opening portion of the contact-hole 44shown in FIG. 15(a) is larger than the diameter β of the bottom thereof.In this case, the rising and falling positions of the secondary electronshown by an upper line are different from the rising and fallingpositions of the compensation current shown by a lower line,repsectively, as shown in FIG. 15(b). Width of a region in which theamount of secondary electron is reduced, which corresponds to theopening diameter α is larger than width of a rectangular region in whichthe compensation current is increased, which corresponds to the bottomdiameter β. By three-dimensionally displaying this together with thedepth d of the contact-hole obtained from the process data, thethree-dimensional configuration of the contact-hole becomes a reversedcone as shown in FIG. 15(c).

[0186] In the case of the tapered contact-hole shown in FIG. 15(a),there may be a case where secondary electron emitted from the taperedportion thereof is detected depending upon a positional relation of theconfiguration of the tapered portion to the secondary electron detector.However, since the aspect ratio of a practical contact-hole is large, itis usual that secondary electron emitted from the inner wall of thecontact-hole is not detected. In FIG. 15(b) and other figures, suchsecondary electron is neglected unless otherwise noticed.

[0187] Linkage with SEM and Slanted Incident Beam

[0188] In a case of a reverse-tapered contact-hole having diameter of anopening portion thereof smaller than a diameter of a bottom portionthereof, it is impossible to distinguish the contact-hole from acontact-hole having an opening diameter equal to a bottom diameter whenvertical electron beam is directed normally thereto. According to thepresent invention, the bottom diameter of the contact-hole is measuredby slanting an incident electron beam with respect to a sample undertest such that electron beam can reach up to a peripheral position of abottom region of the reverse-tapered contact-hole in order to slantelectron beam by a small angle, an electron lens or a deflector forelectron beam scanning is utilized. When electron beam is to be slantedby a large angle, a wafer supporting stage is slanted by rotating itabout a center axis of the wafer. Since it is easily possible to slantthe stage in a range of ±several tens degrees, it is possible to directelectron beam to the reverse-tapered contact-hole at an anglesubstantially equal to a taper angle of the revere-tapered contact-hole.

[0189] FIGS. 16(a) and 16(b), 17(a) and 17(b) and 18(a), 18(b) and 18(c)illustrate examples of measurement of a cylindrical contact-hole, atapered contact-hole and a reverse-tapered contact-hole, respectively,in which FIGS. 16(a), 17(a) and 18(a) shows structure of the respectivecontact-holes and measuring systems therefor, FIGS. 16(a), 17(b) and18(b) show amounts of secondary electron (upper lines) and amounts ofmeasured compensation current (lower lines) with respect to positionsirradiated with electron beam. It Deviations between measuring points ofsecondary electron and compensation current caused by the slantedincident beam are corrected to the positions of the contact-holes. FIG.18(c) shows a three-dimensional configuration of a restoredreverse-tapered contact-hole.

[0190] When the cylindrical contact-hole 43 (FIG. 16(a)) is irradiatedwith slanted electron beam 61 while moving the latter along a centeraxis of the contact-hole, strong secondary electron 32 is observedduring a time for which electron beam 61 irradiates a region of aninsulating film 41 reaches an edge region of the contact-hole 43,secondary electron is reduced sharply. Secondary electron is notobserved during a time for which electron beam 61 irradiates a bottom ofthe contact-hole 43. When electron beam 61 reaches the insulating film41 again on the opposite side of the contact-hole 43, secondary electronis detected again. On the other hand, compensation current is notobserved during a time for which electron beam 61 irradiates theinsulating film 41 and is detected when electron beam 61 reaches theedge of the contact-hole 43. An amount of compensation current issharply increased when electron beam 61 irradiates the bottom of thecontact-hole 43 and sharply reduced when electron beam 61 reaches theinsulating film 41 again.

[0191] For the tapered contact-hole 44 (FIG. 17(a)), considerablesecondary electron is detected during a time for which electron beam 61irradiates an insulating film 41 and is sharply reduced when electronbeam 61 reaches an edge of the contact-hole 44. Substantially nosecondary electron is detected during a time for which electron beam 61irradiates a bottom of the contact-hole 44. When electron beam 61reaches the insulating film 41 again on the opposite side of thecontact-hole 44, secondary electron is observed. On the other hand,compensation current is not detected during a time for which electronbeam 61 irradiates a portion of the insulating film 41 surrounding thecontact-hole 44 and considerable secondary electron is detected during atime for which electron beam 61 irradiates the bottom of thecontact-hole 44. When electron beam 61 irradiates the taper portionagain, compensation current is sharply reduced.

[0192] In the case of the reverse-tapered contact-hole 45 shown in FIG.18(a), a large amount of secondary electron is detected during a timefor which electron beam 61 irradiates the insulating film 42 surroundingthe contact-hole 45 and the amount of secondary electron is sharplyreduced when electron beam 61 reaches the edge of the contact-hole 45.Substantially no secondary electron is detected while electron beam 61irradiates the bottom of the contact-hole 45 and secondary electron isdetected at a time when electron beam 61 starts to irradiate theinsulating film on the opposite side of the contact-hole 45. On theother hand compensation current is not detected when electron beam 61irradiates the surface of the insulating film 42. Compensation currentis detected only a time period for which electron beam 61 irradiates thebottom of the contact-hole 46. When electron beam 61 irradiates theinsulating film 42 or the reverse-tapered portion of the contact-holeagain, compensation current is not detected.

[0193] When the taper angle of the contact-hole coincides with thetilting angle of incident electron beam, increase or decrease of theamount of secondary electron and decrease or increase of compensationcurrent occurs at the same beam irradiating position. Therefore, inorder to obtain a bottom diameter of a reverse-tapered contact-hole, itis necessary to find an incident electron beam angle with whichcompensation current is detected at outermost position by performing anexperiment with using various electron beam incident angles. Since thedepth d of the contact-hole is known, it is possible to obtain adistance from the edge of the opening portion of the contact-hole to theoutermost periphery of the bottom of the contact-hole, which is outsideof the opening portion, from the incident angle of the electron beam andthe depth d of the contact-hole and the bottom diameter of thecontact-hole is calculated by adding the distance value to the diameterof the opening portion. By using this value additionally, thethree-dimensional display of the contact-hole shown in FIG. 18(c) isobtained.

[0194] Detection of Extraordinary Substance

[0195] FIGS. 19(a) to 21(b) illustrate a method for detecting andspecifying an extraordinary substance in a contact-hole, in which FIGS.19(a), 20(a) and 21(a) show structures to be tested and measuringsystems therefor, respectively, and FIGS. 19(b), 20(b) and 21(b) showamounts of measured secondary electron and compensation currents withrespect to the electron beam irradiating position, respectively.

[0196] There may be various extraordinary materials such as dregs ofresist used in etching the contact-hole, particles or dust produced inother processes left on a bottom of the contact-hole. When suchextraordinary substance exists in the contact-hole, the amount of fillersuch as tungsten, aluminum or polysilicon filling the contact-hole as aplug for electrically connecting elements mutually becomes insufficient,resulting in defective contact. Therefore, it is necessary in thesemiconductor process to detect such extraordinary substance prior tothe formation of the plug.

[0197] Since thickness of dust in question is usually 500 Å or moredepending upon material thereof, it prevents incident electron beam fromreaching a bottom of the contact-hole. Therefore, if there is anextraordinary substance on the bottom of the contact-hole, compensationcurrent observed becomes smaller than that produced in a normalcontact-hole.

[0198] In the example shown in FIGS. 19(a) and 19(b), small dust 71exists outside a contact-hole 43 having a constant cross sectional area.When the sample is scanned with vertical thin electron beam 31 generatedby the method shown in FIG. 1 or 2 from a left side position along thecontact-hole 43 in FIG. 19(a), compensation current is not observedduring a time for which electron beam 31 irradiates an insulating film41 surrounding the contact-hole 43. When electron beam 31 reaches anedge of the contact-hole 43, the detection of compensation current isstarted. For a time for which electron beam 31 irradiates a bottom ofthe contact-hole 43, compensation current is observed. When electronbeam 31 irradiates the dust 71, no compensation current is detected. Inthe example shown in FIG. 19(a), the dust 71 is concentrated on one endof the bottom of the contact-hole 43. However, in a case where the dustexists on a center portion of the bottom of the contact-hole andelectron beam 31 passes through a region in which the dust exists,compensation current becomes observed again. FIG. 19(b) shows a resultof measurement of compensation current obtained by changing theirradiating position of electron beam 31. The size of dust 71 can beobtained by comparing the result of measurement with a result ofmeasurement performed for a contact-hole having no dust. Thus, existenceor absence of dust in a contact-hole or size of dust can be detected bymeasuring compensation current.

[0199] FIGS. 20(a) and 20(b) shows an example when dust 72 is depositedon a bottom of a tapered contact-hole 44. When the scanning of thesample with vertical thin electron beam 31 is started from a left sideposition in FIG. 20(a), compensation current is not observed during atime for which electron beam 31 irradiates an insulating film 41surrounding the contact-hole 44. When electron beam 31 irradiates thetapered portion, no compensation is detected since the thickness of theinsulating film is large. On the other hand, when electron beam 31reaches an edge of the contact-hole 44, compensation current isdetected. Although a constant compensation current is detected for atime for which electron beam 31 irradiates a bottom of the contact-hole44, no compensation current is observed when electron beam 31 irradiatesthe dust 72. Existence or absence of dust or size of dust can beobtained by comparing the result of measurement with a result ofmeasurement performed for a contact-hole having no dust.

[0200] FIGS. 21(a) and 21(b) shows an example when dust 73 exists on acenter portion of a bottom of a reverse-tapered contact-hole 45. Whenthe scanning of the sample with electron beam 31 is started,compensation current is not observed during a time for which electronbeam 31 irradiates an insulating film 41 surrounding the contact-hole45. When electron beam 31 reaches the bottom of the contact-hole 45,large compensation current is detected. When electron beam 31 reachesthe dust 73, no compensation current is detected. When electron beam 31passes over the dust 73 and irradiates the bottom of the contact-hole45, compensation current is detected again. When electron beam 31reaches an edge of the contact-hole 45, no compensation current isdetected. The position of the sample, at which no compensation currentis detected, corresponds to a region in which the dust 73 exists and thesize of the dust 73 can be estimated from a width of this region.

[0201] In the dust detection method mentioned above, the ratio ofsecondary electron to the irradiating electron beam (primary electron)depends upon a sample material and has a dependency of irradiatingelectron beam, which is different upon atomic number thereof. Therefore,after the existence or absent of dust in a bottom of a contact-hole isspecified, a variation of compensation current is detected byirradiating the sample with electron beam accelerated by variousacceleration energies. It is possible to specify an object to bemeasured by preliminarily determining the acceleration energy dependencyof compensation current by performing similar experiment for expectedextraordinary substances and obtaining the degree of approximation ofthe acceleration energy dependency by utilizing a technique such asneutral network.

[0202] Measurement with Electron Beam having Large Cross Sectional Area

[0203]FIG. 22(a), 22(b) and 22(c) illustrate an example of measurementutilizing electron beam having a large cross sectional area, in whichFIG. 22(a) is a plan view showing a relation between a contact-hole 81and electron beam 82, FIG. 22(b) is a cross section thereof and FIG.22(c) shows compensation current obtained with respective tocompensation current obtained with respect to the scanning position ofelectron beam and a differentiation thereof.

[0204] In this example, electron beam 82 having rectangular crosssectional area larger than an area of a contact-hole and incident on asample vertically is used. As shown in FIGS. 22(a) and 22(b), the sampleis scanned by electron beam 82 from one side of a sample regioncontaining a single contact-hole 81 to the other while maintaining anirradiation axis vertically with respect to the sample and holding abeam axis fixed. Alternatively, it is possible to scan electron beam 82itself or to move the sample wafer horizontally while fixing theirradiation axis of electron beam 82 at a constant angle with respect tothe sample wafer. Although electron beam 82 used in this case isparallel beam, it is possible to scan the parallel beam by shifting thebeam horizontally by utilizing a pair of deflectors. Magnitude ofcompensation current detected in this case is proportional to an area ofelectron beam irradiating a bottom of the contact-hole 81. Therefore, avalue obtained by differentiating the compensation current indicates anamount of compensation current at a position in the vicinity of a beamedge 83 at which rectangular electron beam 82 is about to be scanned.

[0205] In this example, the scan is performed by gradually shiftingelectron beam 82 such that it irradiates the sample wafer from a regionsurrounding the contact-hole 81 to the bottom of the contact-hole 81 asshown in FIGS. 22(a) and 22(b). There is no compensation currentdetected when electron beam 82 irradiates the region surrounding thecontact-hole 81. When electron beam 82 reaches an edge of the bottom ofthe contact-hole 81, compensation current is increased sharply. Theamount of compensation current is increased gradually during a time whenelectron beam 82 passes the bottom of the contact-hole 81 and becomesmaximum when electron beam 82 covers the whole contact-hole 81. Whenelectron beam 82 passes through the bottom and the other side beam edgereaches the contact-hole 81, compensation current starts to reduce and,when electron beam 82 leaves the region of the contact-hole 81,compensation current disappears.

[0206] A distance between a rising position of the measured compensationcurrent and a peak of a mountain indicating the maximum value ofcompensation current corresponds to a distance between one end of thebottom of the contact-hole 81 and the other end thereof. The distancemeasured by this method corresponds to a distance obtained when a circleis pinched by two parallel lines. Therefore, it is possible to measure aprecise diameter of the circle even when electron beam 82 is not alignedin position precisely with the contact-hole 81.

[0207] Further, assuming that the contact-hole 81 is circular, anincreasing rate of area of a circle becomes maximum in a position of acenter line of the circle. Therefore the position in which theincreasing rate of compensation current becomes maximum corresponds tothe position of the center line of the circle. Consequently, it ispossible to obtain the diameter of the bottom of the contact-hole 81 byperforming a measurement up to the position in which the increasing rateof compensation current becomes maximum, without necessity of scanningthe whole contact-hole 81. That is, it is possible to measure the bottomdiameter of the contact-hole for a time which is substantially a half ofthe time required to scan the whole contact-hole. Further, since thepeak point of the differentiated value is clearly known, the distance isobtained precisely.

[0208] The use of thick electron beam is advantageous in that theconstruction of the electron beam system of the tester is simpler thanthat in a case where thin electron beam is used.

[0209] Measurement using Thin and Thick Electron Beams

[0210]FIGS. 23 and 24 illustrate a measuring method employing acombination of a length measuring mode for precisely measuring a lengthby using thin electron beam and a total measuring mode for obtaining thebottom diameter within a short time by using thick electron beam, inwhich FIG. 23 is a flowchart thereof and FIG. 24 shows an example of apositional relation between a region 92 on a wafer 91 to be measured bythe length measuring mode and a region 93 to be measured by the totalmeasuring mode.

[0211] In the fabrication of semiconductor device, it is necessary tomeasure the bottom diameter of contact-hole precisely at high speed.Generally, in the length measuring mode in which one contact-hole isscanned with a precise thin electron beam and the bottom diameter of thecontact-hole is measured from a distance between positions at which theamount of compensation current is changed, the relative change ofcompensation current is used. Therefore, influence of sophisticatedvariation of the underlying thing is small and the preciseness ofmeasurement of the diameter of contact-hole is high. However, sincevarious information is acquired by performing the fine electron beamscanning for each contact-hole, a considerably long time and aconsiderable amount of data processing are required to perform a test ofa number of contact-holes.

[0212] In order to solve this problem, the length measuring mode forprecisely measuring a length by using thin electron beam and the totalmeasuring mode for obtaining the bottom diameter within a short time byusing thick electron beam are combined. With such combination, it ispossible to keep the preciseness of test high and increase the testspeed.

[0213] Describing the combination of the length measuring mode and thetotal measuring mode in detail with reference to FIGS. 23 and 24, theprecise measurement of bottom diameter is performed for one ofcontact-holes under test or a relatively small number of contact-holes(within a region 92 in which the length measuring mode is to be applied)thereof in the length measuring mode (S11). Then, the total measuringmode is applied to the same contact-hole to obtain a relation betweencompensation current flowing through the contact-hole and the bottomdiameter thereof (S12) to thereby standardize the area in the totalmeasuring mode (S13). The relation between the diameter of thecontact-hole and compensation current in the object to be measured isdetermined by this measurement. Thereafter, the total measuring mode isapplied to other contact-holes (in a region 93 in which the totalmeasuring mode is to be applied) sequentially to measure compensationcurrents for the respective contact-holes (S14) and the measuredcompensation currents are converted into bottom areas or diameters ofthe contact-holes on the basis of the previously obtained relationbetween the compensation current and the bottom diameter of thecontact-hole S15). Thus, it is possible to measure the bottom diameterof contact-hole precisely at high speed.

[0214] Comparative Test of Two Regions

[0215]FIG. 25 shows a construction of an apparatus for performing acomparative test by utilizing two samples under test, FIG. 26 is a testflowchart hereof, FIG. 27 is a figure for explaining the principle ofthe comparative test and FIG. 28 shows a portion of FIG. 27 in enlargedscale.

[0216] A circuit pattern of a semiconductor LSI is fabricated byutilizing an exposing device called “stepper”. Therefore, the intervalbetween adjacent chips or the layout within the chip are made preciselyidentical through the circuit pattern. Describing this with reference toFIGS. 27 and 28, the layout within a chip represented by a relativecoordinates having one of corners of a first sample 101 on a wafer as anoriginal point (0, 0) is to be precisely coincident with the layoutwithin a chip represented by a relative coordinates having one ofcorners of a second sample 102 on the same wafer as an original point(0, 0). These layouts are compared and, when there is a differencetherebetween, which exceeds a certain constant reference, the region isconsidered as containing some abnormality. It is possible to specify aposition of a defective wiring by using such test regardless ofarrangement of a wiring, without necessity of knowing a layoutinformation of the sample from a CAD data. Incidentally, the firstsample 101 and the second sample 102 are formed on one and the samesubstrate and cut away finally as chips.

[0217] In FIG. 25, the apparatus for performing the comparative testincludes an electron gun 112 for producing electron beam verticallyirradiating test samples on a wafer 111, a compensation currentmeasuring electrode 113 on which the wafer 111 is mounted with a bottomsurface thereof in contact with an upper surface of the electrode, an XYstage 114 mounting the electrode 113, for determining a positionalrelation between the wafer 111 on the electrode and electron beamirradiating the wafer, a position detector 115 for precisely measuringthe position of the sample irradiated with electron beam, an irradiatingposition control device 116 for producing a control signal forcontrolling the irradiating position of electron beam on the basis of aresult of detection from the position detector 115 an electron guncontrol device 117 for controlling the electron gun 112 on the basis ofthe control signal from the irradiating position control device 116, astage controller 118 for controlling the XY stage 114 on the basis ofthe control signal from the irradiating position control device 116, acurrent amplifier 119 for amplifying compensation current of theelectrode 113, a D/A converter 120 for converting an output of thecurrent amplifier 119 into a digital signal, a first and second memories121 and 122 for storing the digital signal as current waveformscorrespondingly to positional coordinates, a waveform comparator 123 forcomparing the stored waveforms, a defect detector 124 for determiningthe quality of wiring on the basis of a result of the comparison, adatabase 125 storing an information for determining the quality, adefect position memory 126 for storing positions which are determined asdefective and a defect position output device 127 for displaying and/orprinting the defect position or outputting the defect position to otherprocessors on a network. The irradiating position detector 125 may be,for example, an optical precision distance measurement device.

[0218] Although the memories 121 and 122 for storing waveformscorresponding to the respective chips are shown in FIG. 25 as discretememories, they may be embodied as a common memory. Further, although thedefect position memory 126 is shown in FIG. 25 as an independent memory,it may be possible to provide it by using another memory region of thecommon memory functioning as the memories 121 and 122.

[0219] On demand, the defect position memory 126 can classify defectsand store the position information thereof according to theclassification.

[0220] The electron gun 112 is fixed in a specific position and electronbeam scanning is performed by moving the XY stage 114 with respect tothe position of the electron gun 112 (S21 in FIG. 26). By measuring theposition of the XY stage 114 by means of the electron beam irradiatingposition detector 115, a position to be irradiated with electron beamcan be measured with preciseness of 100 Å. During a time for whichelectron beam scans the first test sample 101 on the wafer 111 along alinear line, current produced in the sample is measured as a firstcurrent waveform by the current amplifier 119 and the D/A converter 120(S22) and the first current waveform is stored in the first memory 121together with the coordinates of the first electron beam irradiatingposition calculated from the position of the XY stage 114 (S23). Thesame measurement is performed for the second test sample 102, which isin a position of an identical pattern to the pattern of the first testsample of another chip, to acquire a second current waveform and thesecond current waveform is stored in the second memory 122 together withthe coordinates of a second electron beam irradiating position (S24 toS26). The quality of the pattern is determined by the qualitydetermination device 124 on the basis of a difference between thecurrent waveforms stored in the first memory 121 and the second memory122, respectively, and a result is stored in the defect position memory125 (S27, S28). On demand, the result is outputted from the defectposition output device 127 to a display or a printer or to other deviceson the network such that the data can be used for other analysis.

[0221] In the case of the measurement using compensation current,electron beam irradiating other portion than the wiring does not causeeffective current unlike the case of the measurement using secondaryelectron. Therefore, noise contained in the detection signal is smallcompared with the case of secondary electron.

[0222] Timing of the comparison between normal chip and defective chipdepends upon memory capacities of the waveform memories 121 and 122. Ina case where the comparison is performed every line, it is enough thatthe waveform memory 121 as well as the waveform memory 122 has a memorycapacity capable of storing a waveform of one line. In a case where,after a normal chip is measured completely, a defect chip is measured,the memory capacity of the waveform memory 121 as web as the waveformmemory 122 has to have a memory capacity capable of store a wholeinformation corresponding to one chip. Since it takes a long time tomove the electron beam irradiating position between chips remote fromeach other by a certain physical distance, it is preferable in order toimprove the test speed to measure one chip after the measurement of apreceding chip is completed, so that it is preferable to use thewaveform memories having memory capacities as large as possible.

[0223] FIGS. 29(a) and 29(b) show a test example, in which FIG. 29(a)shows an example of measurement of a normal chip and FIG. 29(b) shows anexample of measurement of a defective chip. In FIGS. 29(a) and 29(b),left side numerals indicate the line number of electron beam having awidth and each right side letter W indicates the width of electron beamscanning one time. Further, in the lowest line in FIGS. 29(a) and 29(b),compensation currents observed in the fourth electron beam scan relatedto a defective pattern are shown. In this example, it is assumed thatthe size of the wiring under test is constant (for example, 0.15microns) as in the usual semiconductor device. In general, an intervalbetween wiring lines of the semiconductor device is larger than thediameter of the wiring line due to limitation caused by the exposingtechnique and the etching technique. In this example, the wiring linesare arranged randomly and have not a constant periodicity.

[0224] The chips used in FIGS. 29(a) and 29(b) have the naturesdescribed with reference to FIGS. 27 and 28 and are arbitrarily selectedfrom a plurality of chips simultaneously formed on a semiconductorwafer. The chips to be compared with each other depend upon a case.However, it is general that the chips are adjacent ones or that the testis performed by selecting a specific chip, which may be a normal chip,as the first sample, with sequentially changing other chips as thesecond sample. It may be possible to compare test results of three chipsor, more and determine a chip or chips, whose test results indicate anycoincidences with those of the specific chip, as normal chips.

[0225] The quality determination of wiring using electron beam utilizesthe change of magnitude and/or polarity of current produced whenirradiated with electron beam. For simplicity of description, it isassumed here that, since there is a pattern defect in a defectivewiring, current observed for the defective wiring is substantiallysmaller than that observed for the normal wiring.

[0226] The test method will be described in detail. First, the positioncoordinates of a chip, which becomes a sample under test, is madecoincident with a coordinates of a position to be irradiated withelectron beam. Since the size of a wiring of the most recent device asthe test sample is 0.2 microns or less, the alignment is performed withpositional preciseness of 1000 521 or higher with which the positioncoordinates can be reproduced. This is performed by utilizing analignment mark formed on the wafer.

[0227] There are several methods for utilizing the alignment mark. Inone of them, an alignment mark for a mask alignment, which is usuallyutilized in a semiconductor fabrication process. The alignment mark isformed on a surface of a substrate as an oxide film or a metal film andis transformed to a secondary electron image by using a scanningmicroscope provided in the tester. Since a position looked in the imageis just the position irradiated with electron beam, the positioncoordinates of the electron beam scanning system is made coincident withit such that the position of the alignment mark becomes an originalpoint.

[0228] In another method, which does not use the scanning microscope,current flowing through the alignment mark is measured. In such method,a conductor similar to a wiring of a sample under test is formedseparately as an alignment mark. The size of the conductor may besimilar to the size of the wiring or in order to improve the measuringpreciseness, smaller than that of the wiring. Similarly, to theprinciple of the wiring measurement, current observed during a time forwhich electron beam irradiates other portion than the wiring is smalland is increased when the wiring is irradiated with electron beam. Whenthe electron beam irradiating position is coincident with the mark,current observed becomes maximum. This position is utilized as aposition coincident with the alignment.

[0229] After the alignment is completed, line shaped, vertical electronbeam 131 having a length corresponding to the width of the wiring scansthe region of the first test sample, in which the wiring 132 is formed,from left to right along a line “1”. When the electron beam 131 reachesan end of the test region, the irradiation position of the electron beam131 is shifted by a distance corresponding to the width W in a directionperpendicular to the scanning direction and the test sample is scannedwith it along a line “2”. The scanning direction may be S-shape ormeander-shape. Alternatively, the electron beam may be returned to theinitial position and then scan the sample from left to right. The shiftamount W of the electron beam in vertical direction is set to a valuesubstantially equal to the width of the wiring. Similar scanning isperformed along lines “3”, “4”, “5”, “6” and ”7” to scan the whole testsample.

[0230] As shown in FIGS. 29(a) and 29(b), when electron beam reaches aposition corresponding to a wiring 132, which is a normal, current isobserved in the scan along the line “4”. However, there is no currentobserved for a wiring 133, which is defective. That is, an existence ofdefective wiring can be known since the current waveform obtained forthe sample having defective wiring becomes different from that obtainedfor the sample having normal wiring in a region indicated by a referencenumeral 134.

[0231] In the above mentioned test method, it is possible to specify aposition of defective wiring even when the position of wiring in thetest sample is unknown.

[0232] Comparative Test Using Thin Electron Beam

[0233] FIGS. 30(a) and 30(b) show another test example, in which FIG.30(a) shows an example of measurement of a normal chip and FIG. 30(b)shows an example of measurement of a defective chip. In FIGS. 30(a) and30(b), left side numerals indicate the line number of electron beam andcompensation currents observed in the fourth electron beam scan relatedto a defective pattern are shown in lower portions of the respectivefigures.

[0234] When compensation current flowing through a wiring is to bemeasured, compensation current per unit area is the same regardless ofportion of the wiring, which is irradiated with electron beam, if amaterial of the wiring is uniform. Therefore, in order to test thequality of the wiring, it is not always necessary to irradiate the wholewiring with electron beam simultaneously. Further, since the patterndefect occurs in a peripheral portion of the wiring, the defectdetection sensitivity becomes high when the position to be irradiatedwith electron beam is set in the peripheral portion. On the other hand,if the position to be irradiated with electron beam is set to a centerof the wiring, the sensitivity becomes low. In the example shown inFIGS. 30(a) and 30(b), the wiring is scanned with parallel electron beam141 having spot size sufficiently smaller than a width of the wiringwith a scan interval L, which is substantially the same as the width ofthe wiring.

[0235] Similarly to the test shown in FIGS. 29(a) and 29(b), this testcan be performed according to the test flowchart shown in FIG. 26 byusing the device shown in FIG. 25. The electron gun 112 capable ofgenerating parallel electron beam having spot size substantially smallerthan the width of the wiring.

[0236] In this test, an alignment is performed similarly to that in thetest described with reference to FIGS. 29(a) and 29(b), verticalelectron beam 141 having a spot size substantially smaller than thewidth of the wiring scans the region of the first test sample, in whichthe wiring 142 is formed, along a line “1”. Since, as described above,the electron beam irradiating position influences the sensitivity ofdefect detection, the position to be irradiated with electron beam isset in the peripheral portion when high sensitivity is required or in acenter portion of the wiring if the sensitivity can be low. When theelectron beam 141 reaches an end of the test region, the irradiationposition of the electron beam 141 is shifted by a distance correspondingto the scan interval L in a direction perpendicular to the scanningdirection and the test sample is scanned with it along a line “2”. Thescanning direction may be S-shape or the electron beam may be returnedto the initial position and then scan the sample in the same direction.The scan interval L is set to a value substantially equal to the widthof the wiring. Similar scanning is performed along lines “3”, “4”, “5”,“6” and “7” to scan the whole test sample. The above mentionedmeasurement is performed for a second test sample which is an identicalpattern forming location of another chip and respective currentwaveforms are stored correspondingly to coordinates of the electron beamirradiating positions, respectively.

[0237] As shown in FIGS. 30(a) and 30(b), when electron beam reaches aposition corresponding to a wiring 142, which is a normal, current isobserved in the scan along the line “4”. However, there is no currentobserved for a wiring 143, which is defective. By detecting suchdifference of compensation current, it is possible to detect the patterndefect 143 of the wiring.

[0238] Comparative Test Using Line-Shaped Electron Beam

[0239] FIGS. 31(a) and 31(b) illustrate an example in which a pluralityof randomly arranged wiring lines are simultaneously irradiated withelectron beam having a line shaped cross section, in which FIG. 31(a)shows an example of measurement for a normal chip and FIG. 31(b) showsan example of measurement for a defective chip. Electron beam used has arectangular cross section having length of one side in a scan directionis as small as, for example, 100 Å and length of a side perpendicular tothe scan direction is several microns so that it covers a plurality ofwiring lines. An amount of irradiating current of electron beam 165 isin a range from several pA to several nA and acceleration voltagethereof is in a range from several hundreds kV to several thousands kV.

[0240] In the normal sample shown in FIG. 31(a), when electron beam 151reaches a wiring 153 at a position a, current starts to flow. Further,when the electron beam reaches a position b, the current is increasedsince a region of the wiring 152 irradiated thereby is increased. Whenthe electron beam reaches a position c, current is decreased since aregion irradiated thereby is decreased. When the electron beam 151reaches a position d, the electron beam 151 can not irradiate thesample, causing no current to flow. On the other hand, in the defectivesample shown in FIG. 31(b), current obtained in the wiring 154 is small.The current waveform obtained at a position of the defective sample isdifferent from that obtained at an identical position of the normalsample, due to a pattern defect 156 of the defective sample. On theother hand, current waveforms of the normal and defective samplesobtained at positions e, f, g and h at which normal wiring lines 153 and155 are formed are the same.

[0241] As such, when a plurality of wiring lines are irradiated withelectron beam, current produced in each wiring line is measuredindependently and current waveform related to a normal wiring linebecomes substantially different from that relate to a defective wiringline. Therefore, it is possible to detect a defective wiring line bycomparing the current waveform thereof with that of the normal wiringline.

[0242] This test can be done according to the test flowchart shown inFIG. 26 by using the device shown in FIG. 25 as in the case shown inFIGS. 29(a) and 29(b) and FIGS. 30(a) and 30(b). In this test, however,the electron gun 112 generates the line-shaped electron beam.

[0243] FIGS. 32(a) and 32(b) illustrate an example of test for a sampleincluding vertical wiring lines having identical shapes, in which FIG.32(a) shows an example of measurement for a normal chip and FIG. 32(b)shows an example of measurement for a defective chip. Electron beam usedhas a rectangular cross section having length of one side in a scandirection is as small as, for example, 100 Å and length of a sideperpendicular to the scan direction is several microns so that it coversa plurality of wiring lines.

[0244] Current obtainable by the current measuring method, which is theprinciple of measurement of the present invention, is measured as atotal value of currents produced in the wiring lines irradiatedsimultaneously with electron beam. That is, currents produced in therespective wiring lines when irradiated with thin electron beams aremeasured by the line shape electron beam totally.

[0245] In the example shown in FIGS. 32(a) and 32(b), currents producedin the wiring lines 162 and 164 when the electron beam 161 passesthrough a position a to a position b have similar waveforms regardlessof the quality of the samples. On the other hand, when the electron beam161 passes from a position c to a position d, a current produced in thewiring line 163 of the normal sample is observed while current producedin the wiring 165 of the defective sample is small. Therefore, there isa large difference in current waveform between the normal sample and thedefective sample, from which an existence of a pattern defect 166 can bedetected. That is, it is possible to detect a defect and specify aposition of the defect by using the device shown in FIG. 25 and theprocedures shown in FIG. 26 even if positions of wiring lines areoverlapped with respect to the electron beam scanning.

[0246] FIGS. 33(a) and 33(b) illustrate an example of test in a casewhere a wiring having an axis-symmetrical width variation exists, inwhich FIG. 33(a) shows an example of measurement for a normal sample andFIG. 33(b) shows an example of measurement for a defective sample. Inthis test, currents produced in the respective wiring line portions whenirradiated with thin electron beams are measured totally by using aline-shaped electron beam similar to that used in the test shown inFIGS. 32(a) and 32(b).

[0247] For a normal sample shown in FIG. 33(a), current is obtained in awiring 172 when electron beam 171 reaches a position a. On the contrary,no current is observed for a defective sample 173 having a patterndefect 174 even when electron beam 171 reaches a position a as shown inFIG. 33(b). Current produced at a position b in the defective sample 173is small compared with current produced at the position b in the normalsample, due to the pattern defect 174. As described, in the case of thewiring having an axis-symmetrical width variation, there is a differencein current waveform between the normal chip and the defective chip whenthe both chips are measured simultaneously, so that it is possible todetect the defect.

[0248] FIGS. 34(a) and 34(b) illustrate an example of test in a casewhere wiring lines having different widths are arranged randomly, inwhich FIG. 34(a) shows an example of measurement for a normal sample andFIG. 34(b) shows an example of measurement for a defective sample. Whenthese samples are scanned with line-shaped electron beam 181, amounts ofcurrents measured at positions b of the wiring 182 of the normal chipand a wiring 183 of the defective chip, which has a pattern defect 184,are different. By detecting the different, it is possible to detect thedefect.

[0249] Current Waveform Comparison by Integration

[0250] The case where the current waveforms obtained by irradiating thesamples with electron beam are compared directly has been described.However, there are other methods for comparing two current waveforms.

[0251]FIG. 35 shows an example of a construction of a test device forcomparing current waveforms by integrating them and FIG. 36 shows aflowchart used therein. The test device shown in FIG. 35 is similar tothat shown in FIG. 25. Instead of the waveform comparator 123 of thetest device shown in FIG. 25, the test device shown in FIG. 35 includespulse integrators 191 and 192 and an integrated value comparator 193.The pulse integrators 191 and 192 integrate currents produced by onepulse of waveforms acquired by the wiring test, respectively, (S31, S32)and resultant integrated values are compared by the integrated valuecomparator 193 (S27).

[0252] Comparison of Current Value Per Unit Area

[0253] Since positional coordinates of CAD, etc., is not utilized in thecomparison test, electron beam utilized in the test does not alwaysirradiate the wiring completely. Therefore, current value per unit areaof the wiring may be used as a reference.

[0254]FIG. 37 shows an example of a construction of a test device forcomparing current values per unit area, which is similar to the testdevice shown in FIG. 25, and FIG. 38 shows a flowchart thereof. Insteadof the memories 121 and 122 and the waveform comparator 123 of the testdevice shown in FIG. 25, the test device shown in FIG. 37 includes amemory 201, a pulse integrator 202, a pulse width detector 203, adivider 204 and a memory 205. Measured current waveform is stored in thememory 201 (S23 in FIG. 38) and the pulse integrator 202 integrates anamount of current flowing in a time from a rising edge to a falling edgeof one pulse belonging to the stored waveform to obtain a total amountof current flowing during the one pulse (S41). The pulse width detector203 obtains a width of the wiring from the pulse width of the currentwaveform stored in the memory 201 (S42). The divider 204 divides thetotal amount of current obtained by the pulse integrator 202 by thewiring width obtained by the pulse width detector 203, resulting in acurrent value per unit area, which has no relation to the wiring width(S43). A quality determination device 124 compares the value obtained bythe divider 204 with a reference value which is preliminarily obtainedand stored in a quality determination database 125 to determine whetherthe quality of the sample is good or bad according to a difference(S28).

[0255] FIGS. 39(a) and 39(b) illustrate a relation between a coverage ofelectron beam for a wiring and a current waveform, in which FIG. 39(a)is 100% coverage in which electron beam passes through one wiring whilecovering the wiring completely and FIG. 39(b) is 50% coverage in whichelectron beam passes through one wiring while covering a half of thewiring. When the wiring 212 is completely contained in an electron beamscanning band 211, which is a scanning region of the electron beam, anidentical current waveform is obtained every scan. On the contrary, whenthe wiring 212 is deviated from the electron beam scanning band 211, acurrent waveform obtained in the wiring 212 in one scan may becomedifferent from that in another scan. However, since an amount of currentper unit area of a normal contact wiring is constant, it is possible todetermine the quality of a test sample by comparing a current per unitarea obtained by the test sample with the constant current.

[0256] A reference value used in this case for determining the qualityof the test sample is the amount of current per unit area of the normalwiring. Therefore, the reference value may be a value corresponding to awiring of a chip of another wafer processed through an identical step,data obtained from a test pattern or a value obtained by such assimulation, etc. The use of the value corresponding to the wiring of thechip of the other wafer as a reference value is effective when the yieldof wiring in a wafer fabricated in a trial is very low.

[0257] Comparison by Current Value Per Unit Area in Mass-ProductionFactory

[0258]FIG. 40 shows a construction of a semiconductor device tester forperforming a comparative test by using a plurality of chips on one andthe same substrate and FIG. 41 shows a test flowchart used therein. Thesemiconductor device tester is similar to the semiconductor devicetester shown in FIG. 37 and includes two parallel measuring circuitseach similar to the circuit shown in FIG. 37 and including the memory201, the pulse integrator 202, the pulse width detector 203, the divider204 and the memory 205. That is, the semiconductor device tester shownin FIG. 40 includes memories 221 and 231, pulse integrators 222 and 232,pulse width detectors 223 and 233, dividers 224 and 234, memories 225and 235 and a divider 236 for dividing values stored in the memories 225and 235.

[0259] This semiconductor device tester is effectively used in amass-production factory, in which the amount of production is relativelystable, to comparatively test a plurality of chips on a commonsubstrate. That is, the amount of current per unit area, which has norelation to the width of wiring, is obtained by obtaining a currentwaveform by irradiating a first test sample with electron beam, storingthe current waveform the memory 221, obtaining a total amount of currentduring a time from a rising edge to a falling edge of one pulsebelonging to the measured current waveform by integrating the current bythe pulse integrator 222, obtaining a pulse width between the risingedge and the falling edge of the pulse waveform equal to a width of awiring by the pulse width detector 223 and dividing the total amount ofcurrent obtained by the pulse integrator 222 by the pulse width obtainedby the pulse width detector 223. The current per unit area thus obtainedis stored in the memory 225. The same operation is performed for asecond test sample and a resultant current per unit area for the secondtest sample is stored in the memory 235. The content of one of thememories 225 and 235 is divided by the content of the other memory bythe divider 236 and a resultant quotient is compared with a referencevalue preliminarily stored in the quality determination database 125 bythe quality determination device 124. The reference value defines adifference tolerable between chips. When a result of comparison islarge, it is considered that there is a defect in that position.

[0260] Comparison of Position of Current Waveform

[0261]FIG. 42 is a flowchart for determining the quality of wiring byusing a rising and falling edges of an acquired current waveform. Inthis test, the quality of wiring is determined by utilizing the factthat the rising and falling edges of the current waveform corresponds torespective edges of the wiring. That is, a current waveform is acquiredby scanning a first test sample with electron beam (S61, S62), withwhich wiring positions of the first test sample are determined (S63,S64). Then, a current waveform is acquired by scanning a second testsample (S65, S66), with which wiring positions of the second test sampleare determined (S67, S68). A deviation of each wiring position of thefirst test sample from the corresponding wiring position of the secondtest sample is measured by comparing the rising and falling edges of thewaveforms (S69). When the deviation exceeds a constant value, the wiringof the first or second test sample is determined as defective (S70) andthe position of the defective wiring is stored in a memory (S71).

[0262] FIGS. 43(a) and 43(b) show an example of the test, in which FIG.43(a) shows a test result of a normal sample and FIG. 43(b) shows thatof a defective sample. For the normal sample, a wiring 241 is formedperiodically and a rising and falling edges of the current waveform areobserved periodically at electron beam irradiating positions T1 to T8correspondingly to the periodicity of the wiring. For the defectivesample, on the other band, a rising edge of a current waveform at theposition T3 is deviated from that of the normal sample.

[0263]FIG. 44 is a flowchart for determining the quality of wiring byusing a center position of a rising and falling edges of an acquiredcurrent waveform. In this test, a current waveform is acquired byscanning a first test sample with electron beam (S61, S62), with which acenter position of the wiring is determined by calculating centercoordinates between rising and falling coordinates of an acquiredcurrent waveform (S81, S82). Then, a current waveform is acquired byscanning a second test sample (S65, S66), with which a center positionof the wiring is determined by calculating center coordinates betweenrising and falling coordinates of an acquired current waveform (S83,S84). The center position of the wiring of the first test sample iscompared with the center position of the wiring of the second testsample (S85). When the deviation exceeds a constant value (S86), theposition of at least one of the wiring center positions is stored in amemory (S87).

[0264] Electron Beam Sub-Scan

[0265]FIG. 45 shows a construction of a semiconductor device tester forsubstantially improving the test speed when a test is performed byutilizing thin electron beam. In this construction, a deflector 251 forthe sub-scan is included such that a sub-scan by the deflector 251 isperformed simultaneously with a main scan performed by moving a wafer byan XY stage 114.

[0266] Since the main scan is performed by moving the XY stage 114, itis difficult to stably move it at a speed exceeding 1 m/sec by using acurrently available technique. Therefore, even if a processing speed inthe current measuring system is very high, an upper limit of the testspeed is determined by the electron beam scanning speed. In order tosolve this problem, the sub-scan is performed at high speed in adirection perpendicular to the main scan direction simultaneously withthe main scan, such that the scan speed is substantially improved. Sincethe sub scan is performed by deflecting electron beam, the sub scanspeed can be substantially higher than the moving speed of the XY stage.

[0267] When a distance of sub scan is small, an incident angle ofelectron beam is substantially 90 degree and does not affect the test.Therefore, a usual electron beam deflector is utilized therefor. Whenthe distance of sub scan is large, a beam shifter is used therefor inorder to move the beam in parallel.

[0268]FIG. 46 shows an example of a scan locus. A sub scan 253, whichreciprocates with a constant width at high speed, is performed while themain scan 252 progresses with respect to a wiring lines 251 in aconstant direction at low speed. The sub scan 253 is performed inparallel with an interval corresponding to a width of wiring under test.In such case, the scan is performed at an apparent speed, which is themain scan speed multiplied with the sub scan speed, so that the testspeed can be improved by leaps and bounds.

[0269] Speed-Up of Array Region Test

[0270]FIG. 47 is a test flowchart for increasing a test speed. In an SOCdevice, etc., there may be a ray regions, in which long contact wiringlines of such as a memory are arranged equidistantly together withrandom logics. Such array regions are automatically extracted from atest sample without requiring a layout information from a CAD, etc., andthe extracted portion is tested by an independent speed-up methodspecific to the array. In order to do it, it is first to check aninitial chip to acquire current waveforms of all of the regions to betested (S91, S92). Then, positions of wiring lines appearing along thescan direction are detected from rising and falling edges of the currentwaveforms and stored (S93, S94). Thereafter, spacial distribution of thewiring positions is frequency-analyzed every certain specific section(for example, from several tens to several hundreds microns).

[0271]FIG. 48 shows an example of a power spectrum obtained by thefrequency-analysis. The power spectrum has a position dependency. Aregion in which power is large corresponds to a strong correlation tocurrent waveform and an existence of an array is detected in thatregion. On the contrary, a region in which power is small can beconsidered as a random logic region.

[0272] The array portion thus detected is irradiated with electron beamto obtain a rate of defective wiring in the lump. Thus, the test speedis improved.

[0273] Measurement of Three-Dimensional Configuration

[0274] According to the present invention, it is possible to measure notonly the bottom diameter of a contact-hole but also thethree-dimensional configuration thereof. That is, the present inventionutilizes variations and distribution of electron beam irradiating thebottom of the contact-hole by changing acceleration voltage of theelectron beam and the tilting angle of the wafer. This will be describedwith reference to FIGS. 49 and 50. When the acceleration voltage ofelectron beam irradiating a tapered contact-hole 510 is low, electrons513 hardly penetrate an insulating film 512, so that a portion of thewafer other than a bottom portion 514 of the contact-hole 510 hardlyattributes to the current measured as shown in FIG. 49. When theacceleration voltage of electron beam is increased, electrons 513penetrate through a portion 515 of the insulating film 512 surroundingthe bottom portion of the contact-hole 510 as shown in FIG. 50, so thatthe measured current value is changed. By utilizing this phenomenon, itis possible to measure an edge of the contact-hole or a thickness of theinsulating film.

[0275] Similar measurement to that shown in FIGS. 49 and 50 can beperformed for a reverse-tapered contact-hole shown in FIGS. 51 and 52.In such case, as electrons 513 penetrate portions 515 and 516 onaccording to the acceleration voltages, it is impossible to distinguishin configuration of the contact-hole between a tapered contact-hole anda reverse-tapered contact-hole by using only this measurement. In orderto distinguish the contact-hole configuration, the measurement isrepeated while changing the tilting angle of the wafer as shown in FIGS.53 and 54 and, from a change of the intensity distribution of wafercurrent due to the change of the tilting angle, it is possible todetermine whether the contact-hole is tapered or reverse-tapered.

[0276] In order to obtain a three-dimensional configuration of acontact-hole, the dependencies of electron beam absorption coefficientsof materials constituting a sample under test on electron beamacceleration voltage are preliminarily obtained and preserved as alibrary.

[0277] As a method for restoring a three dimensional image from thecurrent values measured, the Fourier transformation, successiveapproximation and superposed integration may be considered. Thesuccessive approximation among them will be described with reference toFIGS. 55 to 58, in which FIG. 55 shows a processing flowchart and FIGS.56 to 58 show respective processings.

[0278] (1) First, as shown in FIG. 56, a two-dimensional image of asample under test is decomposed to M×N pixels and a suitable initialvalue of absorption coefficient is given to the respective pixels(S101).

[0279] (2) Then, absorption coefficients c_(mn) of cells on a locus ofelectron beam irradiation are added (S102). It is assumed here that thefollowing relation is established between the total value of absorptioncoefficients and substrate the current value I measured:

I=I ₀·exp [−Σc _(mn)]  (1)

[0280] In order to establish the above relation, the absorptioncoefficients c_(mn) of the corresponding cells are modified (S103).

[0281] (3) The operation (2) is performed by changing the irradiationangle Θ of electron beam sequentially (S104, S105). That is, theabsorption coefficients c_(mn) of the respective cells are modifiedsequentially such that the equation (1) is always established under anymeasuring condition (any irradiating angle Θ and any accelerationvoltage E).

[0282] (4) The operations (2) and (3) are repeated while sequentiallychanging the acceleration voltage E of electron beam to obtain a map ofan absorption coefficient every acceleration voltage by approximation(S106), as shown in FIG(. 57.

[0283] (5) The dependency of absorption coefficient on accelerationvoltage of each cell is compared with the data on the library as shownin FIG. 58 (S107).

[0284] (6) The quantitative three-dimensional image of the sample undertest is obtain through the above operations (S108).

[0285] In the above described image restoring method, the resolutiondepends upon a probe diameter of electron beam, a spot interval ofelectron beam and a size of the cell in the successive approximationmethod and the preciseness of quantitative analysis depends upon aswinging interval of electron beam acceleration voltage, an amplitude ofthe swinging and a sensitivity of a substrate ammeter.

[0286] Interlayer Deviation

[0287] In the present invention, it is possible to non-destructivelydetect an interlayer deviation by utilizing transmission of electronbeam through an insulating film. That is, a structure of a lower layeris acquired by irradiating a diffusion layer or a wiring with electronbeam passed through the insulating film by increasing the accelerationvoltage and, simultaneously, an information of a diffusion layer or awiring in an upper layer is acquired. It is possible to detect andevaluate a deviation between a contact-hole position and the lower layerstructure from an information of different layers, which is obtainedsimultaneously therewith. Further, by changing a penetration depth ofelectron beam by changing the acceleration voltage, it is possible toevaluate from a surface of a wafer an interlayer deviation such asbetween a second layer and a third layer, between the third layer and afourth layer or between the second layer and the fourth layer. Although,when the lower layer is measured by increasing the acceleration voltage,an information of an upper layer is mixed in the information of thelower information, the information can be separated from each other byan image processing. When an electrically conductive layer such as awiring, which is not electrically connected to the substrate, isarranged in the upper layer, it can be detected as a negative image whenthe lower layer is measured.

[0288] FIGS. 59(a) and 59(b) show an evaluation example of interlayerdeviation, in which FIG. 59(a) shows a cross section of a semiconductordevice, FIG. 59(b) shows a measured current image. In this example, aninsulating film 243 is provided on a wafer 241 on which a diffusionlayer 242 is formed and a portion of the diffusion layer is exposedthrough a contact-hole 244 provided in the insulating film 243. When theacceleration voltage is low and electron beam can not pass through theinsulating film 243, a position of the contact-hole 244 can be knownfrom an irradiating position of electron beam and a measured substratecurrent. When the acceleration voltage is increased to a value withwhich electron beam can pass through the insulating film 243, a positionof the whole diffusion layer 242 can be known from a difference inimpurity density from the substrate. The interlayer deviation can beevaluated by evaluating a deviation between a center of the contact-hole244 and a center of the diffusion layer 242 or a distance between outerperipheries of the contact-hole 244 and the diffusion layer 242.

[0289] FIGS. 60(a) and 60(b) to 61(a) and 61(b) show another evaluationexample of interlayer deviation, in which FIG. 60(a) shows a crosssection of a semiconductor with no interlayer deviation, FIG. 61(a)shows a cross section of a similar semiconductor device with interlayerdeviation and FIGS. 60(b) and 61(b) show respective measured currentimage. On each device, a wiring 252 is provided on a surface of a wafer251 and an insulating layer 253 is formed on the wiring 252. Acontact-hole 254 is formed in the insulating layer 253. Although aposition of the wiring 252 is nominally deviated by d from a position ofthe contact-hole 254, the deviation d′ of the device shown in FIG. 61(a)is larger than the nominal value. Similarly to the example shown inFIGS. 59(a) and 59(b), in the case shown in FIGS. 60(a), 60(b), 61(a)and 61(b), the position of the contact-hole 254 is detected by usingelectron beam having low acceleration voltage and the position of thewiring 252 is detected by electron beam having high accelerationvoltage. By measuring a distance between the contact-hole and thewiring, the deviation can be evaluated.

[0290] In the example shown in FIGS. 62(a), 62(b), a diffusion layer 262is provided on a surface of a wafer 261. A lower layer wiring 264 isformed on a first insulating film 263 which covers the wafer 261 and thediffusion layer 262 and an upper layer wiring 266 is formed on a secondinsulating film 265 which covers the first insulating film 263 and thelower layer wiring 264. The upper layer wiring 266 is covered by a thirdinsulating film 267. Positions of the respective layers can be detectedby measuring the substrate current while changing acceleration voltageof electron beam sequentially.

[0291] In order to detect the interlayer deviations, it is necessary toregulate the acceleration voltage of electron beam such that theelectron beam can reach a desired one of layers. FIG. 63 is a flowchartof the interlayer deviation when main insulating layers are formed ofone material. First, a location in which wiring lines in respectivelayers or diffusion layers are not overlapped is selected on the basisof CAD data and a required magnifying power is determined (S111). Whenthe magnifying power is too high, overlapped area can not monitored and,when the magnifying power is too low, a structure can not be observed.Since, when the magnifying power is too high, there is a possibilitythat an area in which there is no wiring or diffusion layer is testedwastefully, it is preferable to preliminarily select an optimal areafrom a design data so that the determination processing is facilitated.Then, the process data of the respective layers are read in (S112),thickness of insulating layers of the respective layers are calculated(S113), the acceleration voltages corresponding to the thickness of therespective layers are read in from the database (S114) and compensationcurrents are measured at these acceleration voltages (S115). Thismeasurement must be performed for each desired layer.

[0292] If the insulating layers are formed of one material, the reactionof the insulating layers with respect to electron beam is identical.Even when the insulating layers are formed of different materials, it ispossible to handle the different materials of the insulating layers asone material if physical reactions such as secondary electron emissionof the different materials with respect to electron beam are identical.The physical properties of the respective insulating layer materials arepreliminarily measured and stored in the database. The determination ofthe interlayer deviation is determined automatically when the processdata is read in.

[0293] As data to be prepared prior to the regulation of accelerationvoltage, there are compensation current with respect to the kind andthickness of the insulating layer or current value detected in thewiring and compensation current or current detected in the wiring withrespect to acceleration voltage of every kind and thickness of theinsulating layer. These data are preliminarily measured and recorded inthe database. FIG. 64 shows an example of compensation current withrespect to film thickness and FIG. 65 shows an example of compensationcurrent with respect to acceleration voltage.

[0294]FIG. 66 is a measuring flowchart when there are a plurality ofinsulating layers. In this case, a location in which wiring lines inrespective layers or diffusion layers are not overlapped is selected onthe basis of CAD data and a magnifying power required in the measuringregion is determined (S121). Then, thickness of each insulating layer iscalculated on the basis of the process data (S122) and a search isperformed as to whether or not there is, in the database, a settingcoincident with any combination thereof (S123). If there is a coincidentsetting in the database, an acceleration voltage corresponding to atotal thickness of a plurality of different insulating layers is read infrom the database (S124) and compensation current is measured with usingthat acceleration voltage (S125). If thee is no coincident setting, atotal thickness of the insulating layers is calculated on the basis ofthe process data (S126), one of the materials of the insulating layers,which provides the highest resistance against electron beam penetration,is assumed and an acceleration voltage with which electron beam canpenetrate through the insulating layer formed of that material up to thelowest insulating layer of the wafer is obtained (S127). Thereafter,compensation current is measured at acceleration voltage as low as 500 Vand is displayed as an image (S328). With such low acceleration voltage,only a surface layer can be seen. Then, the highest acceleration voltagethus obtained is divided by [(the number of layers)×n] and compensationcurrent is measured at each of acceleration voltages obtained by thisdivision and displayed as images (S129). In this case, n is an optimalone in a range from 1 to 9. An image of a lower layer obtained in thiscase includes an information of an upper layer. The thus obtained imagesare compared (S129) and, when there are images which are coincident(S130), the measurement is performed again by finely changing the usedacceleration voltage. In a case where a second image and a third imageare coincident, the corresponding layers are measured again with usingacceleration voltages which are an intermediate voltage between theacceleration voltages with which a first and second images are obtainedand an intermediate voltage between the acceleration voltages with whichthe third image and a fourth image are obtained (S131). This is repeateduntil the coincident images becomes different images. The measurement isterminated when different images of the layers have obtained from theprocess data(S132).

[0295]FIG. 67 is a flowchart for determining an interlayer deviationafter images of respective layers are obtained. The images of therespective layers (patterns of current images) are compared with thelayout information of CAD data, and the correspondence of each of theimages to one of CAD data, specific wiring or specific diffusion layer,is specified (S141). Then, a coordinates of a position of the thusobtained pattern, which is assigned by CAD data in the design stage isinvestigated and a distance from the upper surface of the wafer to aprojected image is calculated (S142). The actual value obtained by theimage is compared with the ideal value obtained by this calculation. Thedifference corresponds to the interlayer deviation (S143).

[0296] It is possible to acquire the required information in the lump,instead of acquiring information from each of the respective layers bychanging acceleration voltage of electron beam. The acquirement of therequired information of all of the layers in the lump is performedaccording to a measuring flowchart shown in FIG. 68. In this flowchart,a location in which wiring lines in respective layers or diffusionlayers are not overlapped is selected on the basis of CAD data and amagnifying power required in the measuring region is determined (S151)as in the flowchart shown in FIGS. 63 and 65. Then, a total thickness ofthe insulating layers is calculated on the basis of the process data(S152). An acceleration voltage with which electron beam can penetrateto a lowest layer is obtained by assuming one of materials of theinsulating layers, which provides the highest resistance againstelectron beam penetration (S153), and a current image is acquired withthe acceleration voltage (S154). Patterns of the respective layers,which may attribute the current image, are acquired from the CAD dataand are compared with the measured current image (S155). According tothe data obtained from the CAD data, the layers to which the currentimages are belong are classified and an interlayer deviation is obtainedby comparing them with ideal images obtained by the CAD data. Althoughthe classification step of classifying the current images according tothe CAD data is required in this procedure, the preciseness ofmeasurement can be improved since the interlayer deviation can beevaluated by a single image.

[0297] Background Correction

[0298] In the described tests, current produced in a substrate byscanning a sample surface with electron beam is recorded as a functionof electron beam scanning position and by utilizing the function as aluminance signal for image display, a current image is formed on thesubstrate surface. Further, when the image is used in a contact-holetest, the magnitude of current flowing in the contact-hole in a D.C.sense becomes a reference for determining the quality of thecontact-hole. However, an A.C. component is produced since it ispractical that pulsed electron beam irradiates the surface periodicallyor the surface is scanned by electron beam. Therefore, a measuredcurrent contains a capacitive A.C. component in addition to the D.C.component. With such A.C. component, the correspondence betweenbrightness of image and a physical object is broken, so that the qualitydetermination of contact-hole becomes inaccurate and the restoration ofthree-dimensional configuration of the contact-hole becomes difficult.

[0299] In order to solve such problem, it is preferable to measure acurrent by changing an irradiation frequency or scanning frequency ofelectron beam to thereby correct the current component flowing through acapacitance of the sample under test. The processing flowcharts forperforming such correction are shown in FIGS. 69 and 70, respectively.

[0300] In the flowchart shown in FIG. 69, when the sample is irradiatedrepeatedly with pulsed electron beam, a measurement is repeated whilechanging the period of repetition frequency (S161, S163) to obtaincurrent waveforms (S162, S164). The D.C. component is obtained byextrapolating a value measured when the sample is continuouslyirradiated with electron beam from the thus obtained current waveform(S165). Describing this with reference to the semiconductor devicetester shown in FIG. 1, the electron gun 1 produces pulsed electron beamrepeatedly and the repetition frequency of the electron beam is changedby the beam control portion 11. In the data processor 10, the D.C.component is obtained by extrapolating a current value measured when thesample is irradiated continuously with electron beam from the currentmeasured when the sample is irradiated with electron beam at a differentrepetition frequency.

[0301] In the flowchart shown in FIG. 70, a measurement is repeatedwhile changing the scanning speed of electron beam (S171, 173) and, onthe basis of a waveform thus obtained (S172, S174), a value obtainedwhen the scan speed is extrapolated to zero is obtained (S175).Describing this with reference to the semiconductor device tester shownin FIG. 44, the electron beam irradiating position control device 116can switch the scan speed of electron beam through the sub scandeflector 251 and, in the data processor (for example, the block 10 inFIG. 1) to which the output of the D/A converter 120 is supplied, thevalue when the scan speed is extrapolated to zero from the respectivelymeasured current values when the sample is scanned with electron beam atdifferent scan speeds.

[0302] As described in detail, the semiconductor device tester of thepresent invention can obtain an information related to a structure of atest sample in a depth direction thereof non-destructively. Therefore,the present invention is effectively used in a test for determiningwhether or not a quality determination of a fabricated semiconductordevice and/or an optimization of a fabrication process thereof.

[0303] As to a distance information of a cross section of acontact-hole, which can be obtained by only cutting a sample along acenter axis of the contact-hole thereof and looking it by SEM in thepast, it is possible according to the present invention to obtain adistance information of an upper and a lower portions of thecontact-hole by using an information of an opening portion of thecontact-hole, which is obtained from a secondary electron image and aninformation of a bottom configuration of the contact-hole. By furtherusing an information related to a structure of the contact-hole in thedepth direction thereof, which is obtained by using differentacceleration voltages, a more precise information can be obtained.

[0304] When electron beam having a rectangular cross section is used, itis possible to easily specify a position of an edge thereof and toeasily measure an area of a region through which the electron beampasses with high precision. In the described embodiments, the presentinvention has been described when applied to a contact-hole. However,the present invention can be applied to a configuration determinationof, for example, a through-hole, a resist, a wiring and a groove, etc.,which have similar structures to that of a contact-hole. Further, it ispossible to test a configuration and a bottom state of the contact-holeafter etched or washed.

[0305] Since the present invention relates to a non-destructive testmethod, it is possible to obtain the information of a contact-hole in adepth direction without requiring an SEM test of a cross sectionedsurface of a sample. Therefore, it is possible to measure productsdirectly without using a monitor wafer, resulting in reduction ofprocess cost.

[0306] Further, since it is possible to measure in an analog manner anarea and diameter of a bottom of a contact-hole or a three-dimensionalconfiguration thereof at high speed during a process, it is possible toimprove a process in that state. For example, in order to provide theetching condition, it is necessary to control both the openingconfiguration and the bottom configuration of the contact-hole. When thepresent invention is used, it is possible to measure a distribution ofbottom areas of contact-holes of a wafer then and there.

[0307] In the past, it is usual that the quality of contact-hole isdigitally performed with only existence or absence of an opening portionof the contact-hole. Therefore, the abnormality is detected where theopening portion of contact-hole is clogged. According to the presentinvention, however, it is possible to always monitor a diameter of aformed contact-hole in a depth direction. Therefore, it is possible todetect an abnormality of the contact-hole as a change of analog valuerelated to a bottom diameter of the contact-hole and an information of astructure in the depth direction, prior to a defect of the contact-holeopening is actually detected. Therefore, it is possible to take acounter measure against the abnormality quicker compared with the priorart. Particularly, an abnormality is detected by the lump method in thepresent invention to measure the bottom diameter of the contact-hole, itis possible to perform a measurement with higher precision. Since, inthe lump current method, a position of the sample can be regulated suchthat electron beam irradiates one contact-hole, the measurement can beperformed with using lower positional preciseness.

[0308] Since, in the case of the current measurement, only currentflowing in a wiring attributes the measured value, the averaging of testresults, which are required in the conventional test method, becomesunnecessary, so that the test speed can be improved.

[0309] In a case where the interlayer deviation is corrected bymeasuring current flowing in an alignment mask, an expensive secondaryelectron image acquiring device dedicated to the removal of interlayerdeviation becomes unnecessary.

[0310] In the measurement of current waveform in the present invention,it is possible to acquire an information effective in the testregardless of a position of a wiring, through which thick electron beampasses and it is not always necessary to irradiate a specific positionof the wiring with electron beam. On the contrary, it is possible toregulate the detecting sensitivity of defective pattern by changing theelectron irradiating position. Further, since the quality of wiring isdetected by utilizing an edge position information of the wiring, whichis obtained from a rising and falling edges of a current waveformproduced by the electron beam irradiation, there may be a case where atest is possible even when a clear test result can not be obtained fromonly a magnitude change of the acquired current waveform.

[0311] In general, the test speed of wiring lines arranged in an arraycan be improved compared with a case wherein wiring lines are arrangedrandomly. However, it is practical that such arrayed wiring lines andthe random arrangement of wiring lines are mixed in within a chip. Insuch case, the arrangement of wiring is preliminarily checked in aninitial test, estimate a position of the arrayed wiring from a frequencydistribution of measured currents and an optimal test method can beselected on the basis of the position information. Therefore, thespeed-up of the test can be achieved.

[0312] The current waveform measured in the present invention can beperformed by continuously or intermittently irradiating a sample withelectron beam. Further, by performing such scan of electron beam, it ispossible to increase the effective scan speed. Electron beam is notalways required to scan different positions of a sample and it ispossible to scan edge portions of a test region slightly overlapped. Anacceleration voltage and current injection are selected optimallydepending upon a sample to be tested. In a case where the pattern detectis partial, current detected is also proportional to an area of thepartial defect. Therefore, the partial defect can be detected if thevariation of current produced in the partial pattern defect exceeds SNof the tester.

[0313] The measurement of current waveform in the present invention isalso effective in a case where a wiring to be tested is electricallyconnected to a substrate. However, the present is also effective when awiring has a large area or a large leakage current is large or thewiring is electrically connected to the substrate through a largecapacitance. Since it is possible to test a plurality of wiring linessimultaneously, the test speed is high compared with the conventionalmethod. Further, it is possible to monitor a cross sectional structureof a contact-hole from a surface thereof directly.

1-35. (canceled).
 36. A system for obtaining information regarding oneor more contact holes on a semiconductor wafer, the system comprising:an electron gun to irradiate an electron beam, wherein the electron beamincludes a cross-section that is greater than the one or more contactholes; a current measuring device to measure a compensation current,wherein the compensation current is generated in response to theelectron beam irradiated on the one or more contact holes; and a dataprocessor, coupled to the current measuring device, to determineinformation relating to the one or more contact holes using the amountof compensation current measured by the current measuring device. 37.The system of claim 36 further including an electrode, coupled to thecurrent measuring device, wherein the electrode collects thecompensation current.
 38. The system of claim 36 further including anelectrode, coupled to the current measuring device, wherein theelectrode is capacitively coupled to the semiconductor wafer to collectthe compensation current.
 39. The system of claim 36 wherein: theelectron gun irradiates the electron beam at a plurality of electronbeam accelerations; and the current measuring device measures acompensation current generated in response to each electron beam havingone of the plurality of electron beam accelerations.
 40. The system ofclaim 39 wherein the data processor is coupled to the electron gun tocontrol the acceleration voltage of the electron beam.
 41. The system ofclaim 40 wherein the data processor determines information relating tothe one or more contact holes in a depth direction based on changes inthe compensation current measured for the plurality of accelerationvoltages of the electron beam.
 42. The system of claim 40 wherein thedata processor determines information relating to the vertical profileof the one or more contact holes based on changes in the compensationcurrent measured for the plurality of acceleration voltages of theelectron beam.
 43. The system of claim 40 wherein the data processordetermines information relating to the one or more contact holes, in adepth direction, based on changes in the compensation current measuredfor the plurality of acceleration voltages of the electron beam whichare caused by a penetration depth of the electron beam for the pluralityof acceleration voltages.
 44. The system of claim 36 wherein the dataprocessor is coupled to the electron gun to control the accelerationvoltage of the electron beam and the temporal period that the electrongun irradiates the one or more contact holes, and wherein the dataprocessor determines information relating to a vertical profile of theone or more contact holes based on changes in the compensation currentmeasured for the plurality of acceleration voltages of the electronbeam.
 45. The system of claim 36 further including a moveable stagewhich is capable of moving the wafer in at least one direction relativeto the electron beam, and wherein: the electron gun irradiates theelectron beam along a beam axis; and the moveable stage, in response tocontrol signals from the data processor, tilts the wafer relative to thebeam axis.
 46. The system of claim 45 wherein the data processordetermines information relating to the one or more contact holes usingthe compensation current measured for a plurality of incident angles ofthe electron beam on the semiconductor wafer.
 47. The system of claim 36wherein the data processor determines the presence of a residual film inthe one or more contact holes using the amount of the compensationcurrent and a reference value and wherein the reference value isdetermined using a test region having a pattern of one or more contactholes that is similar to the pattern of the one or more contact holes onthe wafer.
 48. A system for obtaining information regarding one or morecontact holes or vias formed in a dielectric film on a semiconductorwafer, the system comprising: an electron gun to irradiate an electronbeam, wherein the electron beam includes a cross-section that is greaterthan the one or more contact holes or vias; a current measuring device,coupled to the semiconductor wafer, to measure a compensation current,wherein the compensation current is generated in response to irradiatingthe electron beam on the one or more contact holes or vias in thedielectric film; and a data processor, coupled to the current measuringdevice, to determine a vertical profile relating to the one or morecontact holes or vias using the compensation current.
 49. The system ofclaim 48 further including an electrode, coupled to the currentmeasuring device, wherein the electrode collects the compensationcurrent.
 50. The system of claim 48 further including an electrode,coupled to the current measuring device, wherein the electrode iscapacitively coupled to the semiconductor wafer to collect thecompensation current.
 51. The system of claim 48 wherein: the electrongun irradiates the electron beam at a plurality of electron beamaccelerations; and the current measuring device measures a compensationcurrent generated in response to each electron beam having one of theplurality of electron beam accelerations.
 52. The system of claim 51wherein the data processor is coupled to the electron gun to control theacceleration voltage of the electron beam.
 53. The system of claim 51wherein: the data processor is coupled to the electron gun to controlthe acceleration voltage of the electron beam and the temporal periodthat the electron gun irradiates the one or more contact holes or vias;and the data processor determines information relating to the verticalprofile of the one or more contact holes or vias based on changes in thecompensation current measured for a plurality of acceleration voltagesof the electron beam.
 54. The system of claim 51 further including amoveable stage which is capable of moving the wafer in at least onedirection relative to the electron beam, and wherein: the electron gunirradiates the electron beam along a beam axis; and the moveable stage,in response to control signals from the data processor, tilts thesemiconductor wafer relative to the beam axis.
 55. The system of claim54 wherein the data processor determines information relating to the oneor more contact holes or vias using the compensation current measuredfor a plurality of incident angles of the electron beam on thesemiconductor wafer.
 56. The system of claim 48 wherein the dataprocessor is coupled to the electron gun to control the temporal periodthat the electron gun irradiates the one or more contact holes.
 57. Thesystem of claim 48 wherein the data processor detects the presence of aresidual film in the one or more contact holes or vias using the amountof the compensation current.
 58. A system for obtaining informationregarding a via formed in a dielectric layer on a semiconductor wafer,the system comprising: an electron gun to irradiate an electron beam onthe via, wherein the electron beam includes a cross-section that isgreater than an aperture of the via; a current measuring device, coupledto the semiconductor wafer, to measure a compensation current, whereinthe compensation current is generated in response to the electron beamirradiated on the via; and a data processor, coupled to the currentmeasuring device, to determine information relating to the via using thecompensation current.
 59. The system of claim 58 wherein: the electrongun irradiates the electron beam at a plurality of electron beamaccelerations; and the current measuring device measures a compensationcurrent generated in response to each electron beam having one of theplurality of electron beam accelerations.
 60. The system of claim 59wherein the data processor is coupled to the electron gun to control theacceleration voltage of the electron beam.
 61. The system of claim 59wherein the data processor determines information relating to the via ina depth direction using differences in the measured compensationcurrents that are in response to changes of acceleration voltages of theelectron beam.
 62. The system of claim 59 wherein the data processordetermines information relating to a vertical profile of the via usingdifferences in the measured compensation currents that are in responseto changes of acceleration voltages of the electron beam.
 63. The systemof claim 59 wherein the data processor is coupled to the electron gun tocontrol the temporal period that the electron gun irradiates the via.64. The system of claim 58 further including a moveable stage which iscapable of moving the wafer in at least one direction relative to theelectron beam, and wherein: the electron gun irradiates the electronbeam along a beam axis; and the moveable stage, in response to controlsignals from the data processor, tilts the semiconductor wafer relativeto the beam axis.
 65. The system of claim 64 wherein the data processordetermines information relating to the via using the compensationcurrent measured for a plurality of incident angles of the electron beamon the semiconductor wafer.
 66. The system of claim 58 wherein the dataprocessor determines the presence of a residual film in the via usingthe compensation current.
 67. The system of claim 58 wherein the dataprocessor determines the presence of a residual film in the via usingthe compensation current and a reference value and wherein the referencevalue is determined using a test region having a via that is similar tothe via in or on the semiconductor wafer.